Add smart toc

Smart table of contents will highlight and expand current section

Fix #1

static/css/style.css

@@ -697,6 +697,9 @@ a.article-title:hover,
   color: #000;
   text-decoration: none;
 }
+.article-toc li a.active {
+  font-weight: bold;
+}
 @media screen and (min-width: 1400px) {
   .article-toc {
     display: block;