ToC: Some HTML improvements and style fixes

The ToC generated broken HTML with unclosed `<li>` tags. This got fixed
as well as some minor optimisation and adding list elements for the
subentries so the elements appear in the ToC while scrolling.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

public/css/extra.css

@@ -93,6 +93,10 @@
     color: #777;
 }
 
+.toc .invisable-node {
+  list-style-type: none;
+}
+
 .ui-toc {
     position: fixed;
     bottom: 20px;