import the ferrocene theme into the repo

Author: pietroalbini

themes/ferrocene/fontawesome.html

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+{# SPDX-License-Identifier: CC-BY-4.0 #}
+{# SPDX-FileCopyrightText: Fonticons, Inc #}
+
+{# To use Font Awesome icons in our templates, we define a macro with the icon
+   name and inline the SVG in it. This way the SVG won't be loaded with a
+   separate request, and it'll be possible to style the icon through CSS. #}
+
+{# Please ensure the SVG you download has "Font Awesome Free" in the comment,
+   not "Font Awesome Pro", otherwise the icon is subject to a proprietary
+   license. If the download from the website is marked as pro, download the SVG
+   from the GitHub repository instead. #}
+
+{% macro icon_search() %}
+    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+        <!--! Font Awesome Free 6.1.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. -->
+        <path d="M500.3 443.7l-119.7-119.7c27.22-40.41 40.65-90.9 33.46-144.7C401.8 87.79 326.8 13.32 235.2 1.723C99.01-15.51-15.51 99.01 1.724 235.2c11.6 91.64 86.08 166.7 177.6 178.9c53.8 7.189 104.3-6.236 144.7-33.46l119.7 119.7c15.62 15.62 40.95 15.62 56.57 0C515.9 484.7 515.9 459.3 500.3 443.7zM79.1 208c0-70.58 57.42-128 128-128s128 57.42 128 128c0 70.58-57.42 128-128 128S79.1 278.6 79.1 208z"/>
+    </svg>
+{% endmacro %}

themes/ferrocene/layout.html

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+{# SPDX-License-Identifier: MIT OR Apache-2.0 #}
+{# SPDX-FileCopyrightText: Ferrous Systems and AdaCore #}
+
+{% extends "basic/layout.html" %}
+{% from "fontawesome.html" import icon_search %}
+
+{% block extrahead %}
+    {{ super() }}
+    <link rel="icon" href="{{ pathto('_static/favicon.svg', 1) }}" sizes="any" type="image/svg+xml" />
+{% endblock %}
+
+{% block content %}
+<div class="wrapper">
+    <div class="sidebar">
+        <header>
+            <a href="{{ pathto('index') }}">
+                <img src="{{ pathto('_static/ferrocene.svg', 1) }}" alt="Ferrocene logo">
+                <h1>{{ shorttitle }}</h1>
+            </a>
+        </header>
+        <form action="{{ pathto('search') }}" method="get" class="side-search">
+            <input type="text" name="q" placeholder="Search...">
+            <button type="submit">{{ icon_search() }}</button>
+        </form>
+        <nav>
+            <label for="toggle-toctree" class="toggle">Toggle navigation</label>
+            <input type="checkbox" id="toggle-toctree">
+            <div class="toctree">
+                {{ toctree(includehidden=false, collapse=false, maxdepth=1) }}
+            </div>
+        </nav>
+    </div>
+    <div class="content">
+        <div class="page">
+            {% block body %}{% endblock %}
+        </div>
+    </div>
+</div>
+<footer>
+    <p>
+        Copyright &copy; {{ copyright }}.
+        {% if theme_license %}
+            Contents released under the {{ theme_license }} license.
+        {% endif %}
+    </p>
+    {% if theme_commit %}
+        <p>Built from commit: <code>{{ theme_commit }}</code></p>
+    {% endif %}
+    <p>Ferrocene is a registered trademark of Critical Section GmbH.</p>
+</footer>
+{% endblock %}
+
+{# The blocks below, defined in the basic layout, are effectively removed from
+   the template as we replace their contents with an empty string. #}
+{% block relbar1 %}{% endblock %}
+{% block relbar2 %}{% endblock %}
+{% block footer %}{% endblock %}

themes/ferrocene/search.html

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+{# SPDX-License-Identifier: MIT OR Apache-2.0 #}
+{# SPDX-FileCopyrightText: Ferrous Systems and AdaCore #}
+
+{% extends "basic/search.html" %}
+
+{% block body %}
+    <noscript>
+        <p>
+            The search functionality requires JavaScript to be enabled!
+            Please enable it to search in the documentation.
+        </p>
+    </noscript>
+    <section id="search-results">
+        <!-- Will be populated by JavaScript -->
+    </section>
+{% endblock %}