Clean up display of revision and build

This will require a patch on RTD side, to pass in `build_id` and `build_url`
in the template context.

sass/_theme_layout.sass

@@ -314,6 +314,13 @@ footer
   color: $gray-light
   p
     margin-bottom: $base-line-height / 2
+  span.commit code
+    padding: 0px
+    font-family: $code-font-family
+    font-size: 1em
+    background: none
+    border: none
+    color: $gray-light
 
 .rst-footer-buttons
   +clearfix

sphinx_rtd_theme/footer.html

@@ -22,9 +22,23 @@
       {%- endif %}
     {%- endif %}
 
-    {%- if last_updated %}
+    {%- if build_id and build_url %}
+      {% trans build_url=build_url, build_id=build_id %}
+        <span class="build">
+          Build
+          <a href="{{ build_url }}">{{ build_id }}</a>.
+        </span>
+      {% endtrans %}
+    {%- elif commit %}
+      {% trans commit=commit %}
+        <span class="commit">
+          Revision <code>{{ commit }}</code>.
+        </span>
+      {% endtrans %}
+    {%- elif last_updated %}
       {% trans last_updated=last_updated|e %}Last updated on {{ last_updated }}.{% endtrans %}
     {%- endif %}
+
     </p>
   </div>
 
@@ -32,9 +46,5 @@
   {% trans %}Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>{% endtrans %}.
   {%- endif %}
 
-  {%- if commit %}
-  Build commit: <code>{{ commit }}</code>
-  {%- endif %}
-
 </footer>