Backport documentation build from master

docs/_templates/layout.html

@@ -1,2 +1,9 @@
-{% set version=github_version %}
 {% extends "!layout.html" %}
+{% block document %}
+{% if version != stable_version %}
+<div class="wy-alert info">
+    <p>You are currently browsing documentation for the <b>{{ version }}</b> branch. Documentation for the stable <b>{{ stable_version }}</b> branch can be found <a href="/{{ stable_version }}/">here</a>.</p>
+</div>
+{% endif %}
+{{ super() }}
+{% endblock %}

docs/_templates/versions.html

@@ -0,0 +1,16 @@
+  <div class="rst-versions" data-toggle="rst-versions" role="note" aria-label="versions">
+    <span class="rst-current-version" data-toggle="rst-current-version">
+      <span class="fa fa-book"> Versions</span>
+      v: {{ version }}
+      <span class="fa fa-caret-down"></span>
+    </span>
+    <div class="rst-other-versions">
+      <dl>
+        <dt>{{ _('Versions') }}</dt>
+        {% for slug, url in versions %}
+          <dd><a href="{{ url }}">{{ slug }}</a></dd>
+        {% endfor %}
+      </dl>
+    </div>
+  </div>
+