Improved markdownlint (#3918)

* Improved markdownlint
* Relaxed rules slighlty
* `npm run markdownlint` for automatic tests
* `npm run markdownlint_fix` for automatic syntax fixing
* Applied the fixes on all our Markdown files

7 files changed, 70 insertions, 75 deletions

diff --git a/docs/en/admins/02_Prerequisites.md b/docs/en/admins/02_Prerequisites.md
index 3c53b33c2..41dabc651 100644
--- a/docs/en/admins/02_Prerequisites.md
+++ b/docs/en/admins/02_Prerequisites.md
@@ -8,12 +8,11 @@ You need to verify that your server can run FreshRSS before installing it. If yo
 | ------------- | ----------------------- | ----------------------- |
 | Web server    | **Apache 2**            | Nginx, lighttpd         |
 | PHP           | **PHP 7+**              |                         |
-| PHP modules   | Required: libxml, cURL, JSON, PDO\_MySQL, PCRE and ctype. <br>Required (32-bit only): GMP <br> Recommended: Zlib, mbstring, iconv, ZipArchive <br> *For the whole modules list see [Dockerfile](https://github.com/FreshRSS/FreshRSS/blob/edge/Docker/Dockerfile-Alpine#L7-L9)* | |
+| PHP modules   | Required: libxml, cURL, JSON, PDO_MySQL, PCRE and ctype.<br />Required (32-bit only): GMP <br />Recommended: Zlib, mbstring, iconv, ZipArchive<br />*For the whole modules list see [Dockerfile](https://github.com/FreshRSS/FreshRSS/blob/edge/Docker/Dockerfile-Alpine#L7-L9)* | |
 | Database      | **MySQL 5.5.3+**        | SQLite 3.7.4+, PostgreSQL 9.5+          |
 | Browser       | **Firefox**             | Chrome, Opera, Safari, or Edge          |
 
-
-# Getting the appropriate version of FreshRSS
+## Getting the appropriate version of FreshRSS
 
 FreshRSS has two different releases. It is better if you spend some time to understand the purpose of each release.
 
diff --git a/docs/en/admins/03_Installation.md b/docs/en/admins/03_Installation.md
index 2a2a886aa..5ef5c62cd 100644
--- a/docs/en/admins/03_Installation.md
+++ b/docs/en/admins/03_Installation.md
@@ -10,7 +10,7 @@ Before you begin, make sure that you've read the [prerequisites](02_Prerequisite
 
 3. Give ownership of the FreshRSS folder to your web server user (often `www-data`). Give group read permissions to all files in `.`[^2], and group write permissions to `./data/`.
 
-4. Install needed PHP modules. A precise and up-to-date list can be found in [the Dockerfile](https://github.com/FreshRSS/FreshRSS/blob/edge/Docker/Dockerfile#L11-L12). 
+4. Install needed PHP modules. A precise and up-to-date list can be found in [the Dockerfile](https://github.com/FreshRSS/FreshRSS/blob/edge/Docker/Dockerfile#L11-L12).
 
 5. Create a database for FreshRSS to use. Note the username and password for this database, as it will be needed during installation!
 
diff --git a/docs/en/admins/07_LinuxUpdate.md b/docs/en/admins/07_LinuxUpdate.md
index c1b2da5f5..6323c2a1a 100644
--- a/docs/en/admins/07_LinuxUpdate.md
+++ b/docs/en/admins/07_LinuxUpdate.md
@@ -24,87 +24,76 @@ You may wish to run the cron task or systemd unit (`freshrss.service`) immediate
 
 **You must have used git to install FreshRSS to use this update method.**
 
-If your local user doesn't have write access to the FreshRSS folder, use a sudo shell (`sudo -s`), prefix the following commands with `sudo `, or switch to an account that does have write access to the folder.
+If your local user doesn't have write access to the FreshRSS folder, use a sudo shell (`sudo -s`), prefix the following commands with `sudo`, or switch to an account that does have write access to the folder.
 
 1. Change to your FreshRSS directory
-
-```sh
-cd /usr/share/FreshRSS/
-```
+	```sh
+	cd /usr/share/FreshRSS/
+	```
 
 2. Fetch the most recent code from GitHub
-
-```sh
-git fetch --all
-```
+	```sh
+	git fetch --all
+	```
 
 3. Discard manual changes and delete manual additions
+	```sh
+	git reset --hard
+	git clean -f -d
+	```
 
-```sh
-git reset --hard
-git clean -f -d
-```
-
-Note: If you wish to keep your changes, it's better to [create a pull request](https://github.com/FreshRSS/FreshRSS/compare) or [an extension](../developers/03_Backend/05_Extensions.md).
+	Note: If you wish to keep your changes, it's better to [create a pull request](https://github.com/FreshRSS/FreshRSS/compare) or [an extension](../developers/03_Backend/05_Extensions.md).
 
 4. Update FreshRSS
+	```sh
+	git checkout edge
+	git pull
+	git checkout $(git describe --tags --abbrev=0)
+	```
 
-```sh
-git checkout edge
-git pull
-git checkout $(git describe --tags --abbrev=0)
-```
-
-Note: If you want to use the rolling release, the last command is optional.
+	Note: If you want to use the rolling release, the last command is optional.
 
 5. (optional) Make sure you use the correct version
+	```sh
+	git status
+	```
 
-```sh
-git status
-```
-
-The command should tell you the tag that you're using. It must be the same as the one associated with [the latest release on GitHub](https://github.com/FreshRSS/FreshRSS/releases/latest). If you use the rolling release, it should tell you that your `edge` branch is up to date with `origin`.
+	The command should tell you the tag that you're using. It must be the same as the one associated with [the latest release on GitHub](https://github.com/FreshRSS/FreshRSS/releases/latest). If you use the rolling release, it should tell you that your `edge` branch is up to date with `origin`.
 
 6. Re-set correct permissions so that your web server can access the files
-
-```sh
-chown -R :www-data . && chmod -R g+r . && chmod -R g+w ./data/
-```
+	```sh
+	chown -R :www-data . && chmod -R g+r . && chmod -R g+w ./data/
+	```
 
 ## Using the Zip archive
 
 If your local user doesn't have write access to the FreshRSS folder, use a sudo shell (`sudo -s`), prefix the following commands with `sudo`, or switch to an account that does have write access to the folder.
 
 1. Change to your FreshRSS directory
-
-```sh
-cd /usr/share/FreshRSS/
-```
+	```sh
+	cd /usr/share/FreshRSS/
+	```
 
 2. Get the link to the Zip archive for [the latest release](https://github.com/FreshRSS/FreshRSS/releases/latest): [`https://github.com/FreshRSS/FreshRSS/archive/latest.zip`](https://github.com/FreshRSS/FreshRSS/archive/latest.zip). If you want to use the rolling release, the link is [`https://github.com/FreshRSS/FreshRSS/archive/edge.zip`](https://github.com/FreshRSS/FreshRSS/archive/edge.zip).
 
 3. Download and unzip the update file
-
-```sh
-wget -O freshrss.zip https://github.com/FreshRSS/FreshRSS/archive/latest.zip
-unzip freshrss.zip
-```
-
-3. Overwrite all your existing files with the new ones
-
-```sh
-cp -R FreshRSS-*/* .
-```
-
-4. Re-set permissions
-
-```sh
-chown -R :www-data . && chmod -R g+r . && chmod -R g+w ./data/
-```
-
-5. Clean up the FreshRSS directory by deleting the downloaded zip, the file forcing the setup wizard and the temporary directory
-
-```sh
-rm -f freshrss.zip
-rm -rf FreshRSS-*/
-```
+	```sh
+	wget -O freshrss.zip https://github.com/FreshRSS/FreshRSS/archive/latest.zip
+	unzip freshrss.zip
+	```
+
+4. Overwrite all your existing files with the new ones
+	```sh
+	cp -R FreshRSS-*/* .
+	```
+
+5. Re-set permissions
+	```sh
+	chown -R :www-data . && chmod -R g+r . && chmod -R g+w ./data/
+	```
+
+6. Clean up the FreshRSS directory by deleting the downloaded zip, the file forcing the setup wizard and the temporary directory
+	```sh
+	rm -f freshrss.zip
+	rm -rf FreshRSS-*/
+	```
diff --git a/docs/en/admins/08_FeedUpdates.md b/docs/en/admins/08_FeedUpdates.md
index ef79d6351..a2e8e7ce6 100644
--- a/docs/en/admins/08_FeedUpdates.md
+++ b/docs/en/admins/08_FeedUpdates.md
@@ -7,6 +7,7 @@ FreshRSS is updated by the `./app/actualize_script.php` script. Knowing this, we
 **Note:** the following examples assume that FreshRSS is installed to `/usr/share/FreshRSS`. You'll need to modify the FreshRSS path to reflect your own system.
 
 **Note:** If you cannot configure a local Cronjob, [see an alternative using online cron](../users/03_Main_view.md#online-cron).
+
 ## Cron as a trigger
 
 You'll need to check the Cron documentation for your specific distribution ([Debian/Ubuntu](https://help.ubuntu.com/community/CronHowto), [Red Hat/Fedora/CentOS](https://fedoraproject.org/wiki/Administration_Guide_Draft/Cron), [Slackware](https://docs.slackware.com/fr:slackbook:process_control?#cron), [Gentoo](https://wiki.gentoo.org/wiki/Cron), [Arch Linux](https://wiki.archlinux.org/index.php/Cron) ...) to make sure you set the Cron job correctly.
@@ -14,10 +15,11 @@ You'll need to check the Cron documentation for your specific distribution ([Deb
 It's advisable that you run the Cron job as your Web server user (often `www-data`).
 
 ### Example on Debian/Ubuntu
+
 To run the updater script every hour, and 10 minutes past the hour:
 
 Run `sudo crontab -e` and copy the following line into the crontab:
-```
+```text
 10 * * * * www-data php -f /usr/share/FreshRSS/app/actualize_script.php > /tmp/FreshRSS.log 2>&1
 ```
 
@@ -27,7 +29,7 @@ Some systems can't use a Cron job, but they can use systemd. It's easy to config
 
 First you need to add a `freshrss.timer` file in `/etc/systemd/system/` with the following content:
 
-```
+```ini
 [Unit]
 Description=FreshRSS get new content
 
@@ -43,7 +45,7 @@ This timer will start 30 seconds after boot and it will trigger the service ever
 
 Then you need to add a `freshrss.service` file in the same directory. This will be the description of the service triggered by the aforementioned timer.
 
-```
+```ini
 [Unit]
 Description=FreshRSS get new content
 Wants=freshrss.timer
diff --git a/docs/en/admins/09_AccessControl.md b/docs/en/admins/09_AccessControl.md
index fabbffdf3..8ee193cea 100644
--- a/docs/en/admins/09_AccessControl.md
+++ b/docs/en/admins/09_AccessControl.md
@@ -4,7 +4,8 @@ FreshRSS offers three methods of Access control: Form Authentication using JavaS
 
 ## Form Authentication
 
-Form Authentication requires the use of JavaScript. It will work on any supported version of PHP, but version 5.5 or newer is recommended (see footnote 1 in [prerequisites](02_Prerequisites.md) for the reason why).
+Form Authentication requires the use of JavaScript. It will work on any supported version of PHP,
+but version 5.5 or newer is recommended (see footnote 1 in [prerequisites](02_Prerequisites.md) for the reason why).
 
 This option requires nothing more than selecting Form Authentication during installation.
 
@@ -22,7 +23,9 @@ When using auto-registration, you can optionally use the `http_auth_auto_registe
 variable containing the email address of the authenticated user (e.g. `REMOTE_USER_EMAIL`).
 
 ## No Authentication
-Not using authentication on your server is dangerous, as anyone with access to your server would be able to make changes as an admin. It is never advisable to not use any form of authentication, but **never** chose this option on a server that is able to be accessed outside of your home network.
+
+Not using authentication on your server is dangerous, as anyone with access to your server would be able to make changes as an admin.
+It is never advisable to not use any form of authentication, but **never** chose this option on a server that is able to be accessed outside of your home network.
 
 ## Hints
 
diff --git a/docs/en/admins/10_ServerConfig.md b/docs/en/admins/10_ServerConfig.md
index 5286023f8..6c5823a2d 100644
--- a/docs/en/admins/10_ServerConfig.md
+++ b/docs/en/admins/10_ServerConfig.md
@@ -1,9 +1,10 @@
 # Apache/Nginx Configuration Files
 
 ## Apache configuration
+
 This is an example Apache virtual hosts configuration file. It covers HTTP and HTTPS configuration.
 
-```
+```apache
 <VirtualHost *:80>
 	DocumentRoot /var/www/html/
 
@@ -62,7 +63,8 @@ This is an example Apache virtual hosts configuration file. It covers HTTP and H
 This is an example nginx configuration file. It covers HTTP, HTTPS, and php-fpm configuration.
 
 You can find simpler config file but they may be incompatible with FreshRSS API.
-```
+
+```nginx
 server {
 	listen 80;
 	listen 443 ssl;
diff --git a/docs/en/admins/11_Themes.md b/docs/en/admins/11_Themes.md
index 6ee26d955..c4edb841a 100644
--- a/docs/en/admins/11_Themes.md
+++ b/docs/en/admins/11_Themes.md
@@ -4,14 +4,14 @@
 
 **For small theme changes, the official [CustomCSS extension](https://github.com/FreshRSS/Extensions) is recommended.**
 
-Themes should be installed at `FreshRSS/p/themes/theme-name`. Docker users can use 
+Themes should be installed at `FreshRSS/p/themes/theme-name`. Docker users can use:
 
+```sh
+-v /home/you/my-theme/:/var/www/FreshRSS/p/themes/my-theme/
 ```
-  -v /home/you/my-theme/:/var/www/FreshRSS/p/themes/my-theme/
-``` 
 
-or a similar method to add their theme to their FreshRSS instance. 
+or a similar method to add their theme to their FreshRSS instance.
 
-# Creating themes
+## Creating themes
 
 Information on creating themes can be found in [the developer documentation.](../developers/04_Frontend/02_Design.md)