Style headerlinks for table captions properly

Fixes #437

Author: mitya57

sass/_theme_rst.sass

@@ -108,7 +108,7 @@
     @extend h2
 
   // 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, p.caption
+  h1, h2, h3, h4, h5, h6, dl dt, p.caption, table > caption
     .headerlink
       display: none
       visibility: hidden