Make doc headers clickable again

...without preventing clicks on other things.

Just use an `<a name="...">` tag that doesn't take up any space to make sure that we're not covering up something else.

For whatever reason, doing `position: relative; top: -$navHeight;` doesn't work and causes the anchor target not to be moved up. This solution works in both Chrome and Firefox.

_css/react.scss

@@ -77,21 +77,19 @@ li {
 // Make header navigation linkable and on the screen. Used in documentation and
 // blog posts.
 h1, h2, h3, h4, h5, h6 {
-  &.anchor {
-    position: relative;
-    top: -$navHeight;
-    z-index: -1;
-    > a {
-      color: $darkTextColor;
-      position: relative;
-      top: $navHeight;
+  .anchor {
+    margin-top: -$navHeight;
+    position: absolute;
+  }
 
-      &:hover {
-        text-decoration: underline;
-      }
-    }
+  &:hover .hash-link {
+    display: inline;
   }
 }
+.hash-link {
+  color: $mediumTextColor;
+  display: none;
+}
 
 // Main Nav
 

_plugins/header_links.rb

@@ -11,7 +11,7 @@ class Redcarpet::Render::HTML
       .gsub(/\s+/, "-")
       .gsub(/[^A-Za-z0-9\-_.]/, "")
 
-    return "<h#{level} id=\"#{clean_title}\" class=\"anchor\"><a href=\"##{clean_title}\">#{title}</a></h#{level}>"
+    return "<h#{level}><a class=\"anchor\" name=\"#{clean_title}\"></a>#{title} <a class=\"hash-link\" href=\"##{clean_title}\">#</a></h#{level}>"
   end
 end