Style headerlinks for table captions properly (readthedocs#454)

* Style headerlinks for table captions properly

Fixes readthedocs#437

* Make .headerlink code work with center-aligned elements

* Lowered font size for table headerlink as requested in the review

Author: mitya57

sass/_theme_rst.sass

@@ -106,19 +106,19 @@
     @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
       font-size: 14px
       @extend .fa
       &:after
-        visibility: visible
         content: "\f0c1"
         font-family: FontAwesome
-        display: inline-block
-    &:hover .headerlink
-      display: inline-block
+    &:hover .headerlink:after
+      visibility: visible
+
+  table > caption .headerlink:after
+    font-size: 12px
 
   .centered
     text-align: center