API docs: migrate to corporate design (#968)

* API docs: migrate to corporate design
* Minor docs fixes

Author: robsdedude

docs/source/_static/anchor_new_target.js

@@ -0,0 +1,7 @@
+{%- extends "layout.html" %}
+{% set title = _('Tree') %}
+
+{% block body %}
+<h1>{{ _('Tree') }}</h1>
+{{ toctree(includehidden=True, collapse=False, maxdepth=-1) }}
+{% endblock %}

docs/source/_static/custom.css

@@ -0,0 +1,18 @@
+<div id="indexlinkbox">
+    <h3 id="indexlinklabel">{{ _('Index') }}</h3>
+
+    <div class="indexlinkwrapper nav-menu">
+        <ul>
+            <li class="toctree-l1">
+                <a href="{{ pathto('genindex')|e }}" class="indexlink genindex">
+                    {{ _('Alphabetical') }}
+                </a>
+            </li>
+            <li class="toctree-l1">
+                <a href="{{ pathto('gentree')|e }}" class="indexlink gentree">
+                    {{ _('Tree') }}
+                </a>
+            </li>
+        </ul>
+    </div>
+</div>