Improve layout of documentation page and add search feature (#8247)

* Improve layout of documentation page and add search feature

Closes https://github.com/FreshRSS/FreshRSS/issues/7915, https://github.com/FreshRSS/FreshRSS/issues/5325

Also: anchor headings and fix building site locally

* Further improvements

* Set color of hyperlinks
* Consistent styling of close aside button across devices
* Mobile layout 600px -> 1200px
* Add suffix to docs `<title>`
    * Note: titles of pages probably need to be improved, since currently they are just derived from the names of the first heading on every page
* Add favicon

* Improve font

* Try to fix favicon not loading correctly on GH pages

* Use local font

* Attempt to fix GH pages

* Final improvements

* Copy to clipboard button
* Support for nojs search
* Dark mode
* Load search.json (200KB json) only on search input focus
* Keep scroll state of sidebar across navigations

* Clickable images and CSP

CSP so we avoid hotlinking resources and clickable images are useful for zooming on mobile for example

* Fix typos

* Disable Dark Reader extension if dark mode CSS is loaded

* Support internationalisation (via language dropdown)

* Add Gemfile.lock

* Make CI build work with the custom plugin

* Make menus closable with Esc

* Fix typos CI

* Suggestions

* Use `ruby/setup-ruby` action in workflow for installing and caching gems.

* Run build only when there are changes to `docs/`

See: https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows?versionId=free-pro-team%40latest&productId=actions#running-your-workflow-only-when-a-push-to-specific-branches-occurs

* Change font to `Open Sans`

* Increase line height

* Fix Liquid syntax error

1 files changed, 174 insertions, 0 deletions

diff --git a/docs/_includes/anchor_headings.html b/docs/_includes/anchor_headings.html
new file mode 100644
index 000000000..ee5c2a640
--- /dev/null
+++ b/docs/_includes/anchor_headings.html
@@ -0,0 +1,174 @@
+{% capture headingsWorkspace %}
+  {% comment %}
+    Copyright (c) 2018 Vladimir "allejo" Jimenez
+
+    Permission is hereby granted, free of charge, to any person
+    obtaining a copy of this software and associated documentation
+    files (the "Software"), to deal in the Software without
+    restriction, including without limitation the rights to use,
+    copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following
+    conditions:
+
+    The above copyright notice and this permission notice shall be
+    included in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+    OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+    OTHER DEALINGS IN THE SOFTWARE.
+  {% endcomment %}
+  {% comment %}
+    Version 1.0.13
+      https://github.com/allejo/jekyll-anchor-headings
+
+    "Be the pull request you wish to see in the world." ~Ben Balter
+
+    Usage:
+      {% include anchor_headings.html html=content anchorBody="#" %}
+
+    Parameters:
+      * html          (string) - the HTML of compiled markdown generated by kramdown in Jekyll
+
+    Optional Parameters:
+      * beforeHeading (bool)   : false  - Set to true if the anchor should be placed _before_ the heading's content
+      * headerAttrs   (string) :  ''    - Any custom HTML attributes that will be added to the heading tag; you may NOT use `id`;
+                                          the `%heading%` and `%html_id%` placeholders are available
+      * anchorAttrs   (string) :  ''    - Any custom HTML attributes that will be added to the `<a>` tag; you may NOT use `href`, `class` or `title`;
+                                          the `%heading%` and `%html_id%` placeholders are available
+      * anchorBody    (string) :  ''    - The content that will be placed inside the anchor; the `%heading%` placeholder is available
+      * anchorClass   (string) :  ''    - The class(es) that will be used for each anchor. Separate multiple classes with a space
+      * anchorTitle   (string) :  ''    - The `title` attribute that will be used for anchors
+      * h_min         (int)    :  1     - The minimum header level to build an anchor for; any header lower than this value will be ignored
+      * h_max         (int)    :  6     - The maximum header level to build an anchor for; any header greater than this value will be ignored
+      * bodyPrefix    (string) :  ''    - Anything that should be inserted inside of the heading tag _before_ its anchor and content
+      * bodySuffix    (string) :  ''    - Anything that should be inserted inside of the heading tag _after_ its anchor and content
+      * generateId    (true)   :  false - Set to true if a header without id should generate an id to use.
+
+    Output:
+      The original HTML with the addition of anchors inside of all of the h1-h6 headings.
+  {% endcomment %}
+
+  {% assign minHeader = include.h_min | default: 1 %}
+  {% assign maxHeader = include.h_max | default: 6 %}
+  {% assign beforeHeading = include.beforeHeading %}
+  {% assign headerAttrs = include.headerAttrs %}
+  {% assign nodes = include.html | split: '<h' %}
+
+  {% capture edited_headings %}{% endcapture %}
+
+  {% for _node in nodes %}
+    {% capture node %}{{ _node | strip }}{% endcapture %}
+
+    {% if node == "" %}
+      {% continue %}
+    {% endif %}
+
+    {% assign nextChar = node | replace: '"', '' | strip | slice: 0, 1 %}
+    {% assign headerLevel = nextChar | times: 1 %}
+
+    <!-- If the level is cast to 0, it means it's not a h1-h6 tag, so let's see if we need to fix it -->
+    {% if headerLevel == 0 %}
+      <!-- Split up the node based on closing angle brackets and get the first one. -->
+      {% assign firstChunk = node | split: '>' | first %}
+
+      <!-- If the first chunk does NOT contain a '<', that means we've broken another HTML tag that starts with 'h' -->
+      {% unless firstChunk contains '<' %}
+        {% capture node %}<h{{ node }}{% endcapture %}
+      {% endunless %}
+
+      {% capture edited_headings %}{{ edited_headings }}{{ node }}{% endcapture %}
+      {% continue %}
+    {% endif %}
+
+    {% capture _closingTag %}</h{{ headerLevel }}>{% endcapture %}
+    {% assign _workspace = node | split: _closingTag %}
+    {% capture _hAttrToStrip %}{{ _workspace[0] | split: '>' | first }}>{% endcapture %}
+    {% assign header = _workspace[0] | replace: _hAttrToStrip, '' %}
+    {% assign escaped_header = header | strip_html | strip %}
+
+    {% assign _classWorkspace = _workspace[0] | split: 'class="' %}
+    {% assign _classWorkspace = _classWorkspace[1] | split: '"' %}
+    {% assign _html_class = _classWorkspace[0] %}
+
+    {% if _html_class contains "no_anchor" %}
+      {% assign skip_anchor = true %}
+    {% else %}
+      {% assign skip_anchor = false %}
+    {% endif %}
+
+    {% assign _idWorkspace = _workspace[0] | split: 'id="' %}
+    {% if _idWorkspace[1] %}
+      {% assign _idWorkspace = _idWorkspace[1] | split: '"' %}
+      {% assign html_id = _idWorkspace[0] %}
+      {% assign h_attrs = headerAttrs %}
+    {% elsif include.generateId %}
+      <!-- If the header did not have an id we create one. -->
+      {% assign html_id = escaped_header | slugify %}
+      {% if html_id == "" %}
+        {% assign html_id = false %}
+      {% endif %}
+      <!-- Append the generated id to other potential header attributes. -->
+      {% capture h_attrs %}{{ headerAttrs }} id="%html_id%"{% endcapture %}
+    {% endif %}
+
+    <!-- Build the anchor to inject for our heading -->
+    {% capture anchor %}{% endcapture %}
+
+    {% if skip_anchor == false and html_id and headerLevel >= minHeader and headerLevel <= maxHeader %}
+      {% if h_attrs %}
+        {% capture _hAttrToStrip %}{{ _hAttrToStrip | split: '>' | first }} {{ h_attrs | strip | replace: '%heading%', escaped_header | replace: '%html_id%', html_id }}>{% endcapture %}
+      {% endif %}
+
+      {% capture anchor %}href="#{{ html_id }}"{% endcapture %}
+
+      {% if include.anchorClass %}
+        {% capture anchor %}{{ anchor }} class="{{ include.anchorClass }}"{% endcapture %}
+      {% endif %}
+
+      {% if include.anchorTitle %}
+        {% capture anchor %}{{ anchor }} title="{{ include.anchorTitle | replace: '%heading%', escaped_header }}"{% endcapture %}
+      {% endif %}
+
+      {% if include.anchorAttrs %}
+        {% capture anchor %}{{ anchor }} {{ include.anchorAttrs | replace: '%heading%', escaped_header | replace: '%html_id%', html_id }}{% endcapture %}
+      {% endif %}
+
+      {% capture anchor %}<a {{ anchor }}>{{ include.anchorBody | replace: '%heading%', escaped_header | default: '' }}</a>{% endcapture %}
+
+      <!-- In order to prevent adding extra space after a heading, we'll let the 'anchor' value contain it -->
+      {% if beforeHeading %}
+        {% capture anchor %}{{ anchor }} {% endcapture %}
+      {% else %}
+        {% capture anchor %} {{ anchor }}{% endcapture %}
+      {% endif %}
+    {% endif %}
+
+    {% capture new_heading %}
+<h{{ _hAttrToStrip }}
+  {{ include.bodyPrefix }}
+  {% if beforeHeading %}
+    {{ anchor }}{{ header }}
+  {% else %}
+    {{ header }}{{ anchor }}
+  {% endif %}
+  {{ include.bodySuffix }}
+</h{{ headerLevel }}>
+    {% endcapture %}
+
+    <!--
+    If we have content after the `</hX>` tag, then we'll want to append that here so we don't lost any content.
+    -->
+    {% assign chunkCount = _workspace | size %}
+    {% if chunkCount > 1 %}
+      {% capture new_heading %}{{ new_heading }}{{ _workspace | last }}{% endcapture %}
+    {% endif %}
+
+    {% capture edited_headings %}{{ edited_headings }}{{ new_heading }}{% endcapture %}
+  {% endfor %}
+{% endcapture %}{% assign headingsWorkspace = '' %}{{ edited_headings | strip }}