Add support for Sphinx 1.3 toctree captions

Reuses styling for wy-nav-vertical headers, which seem to be unused, with some
color changes to the header elements. Also fixes caption headerlink styling.

demo_docs/source/index.rst

@@ -18,6 +18,11 @@ Contents:
 
     demo
     list
+
+.. toctree::
+    :maxdepth: 2
+    :caption: This is an incredibly long caption for a long menu
+
     long
 
 Maaaaath!

sass/_theme_layout.sass

@@ -24,16 +24,17 @@
     padding: 0 $base-font-size
 
 .wy-menu-vertical
-  header
+  header, p.caption
     height: $base-font-size * 2
     display: inline-block
     line-height: $base-font-size * 2
     padding: 0 $gutter
+    margin-bottom: 0
     display: block
     font-weight: bold
     text-transform: uppercase
     font-size: 80%
-    color: $menu-logo-color
+    color: $gray
     white-space: nowrap
 
   ul

sass/_theme_rst.sass

@@ -99,7 +99,7 @@
     display: block
 
   // This is the #href that shows up on hover. Sphinx's is terrible so I hack it away.
-  h1, h2, h3, h4, h5, h6, dl dt
+  h1, h2, h3, h4, h5, h6, dl dt, p.caption
     .headerlink
       display: none
       visibility: hidden