fold markdown's headings

Author: daiyam

lib/main.html

@@ -117,6 +117,7 @@
   <script src="../node_modules/codemirror/addon/search/jump-to-line.js"></script>
 
   <script src="../node_modules/codemirror/addon/fold/brace-fold.js"></script>
+  <script src="../node_modules/codemirror/addon/fold/markdown-fold.js"></script>
   <script src="../node_modules/codemirror/addon/fold/foldgutter.js"></script>
   <script src="../node_modules/codemirror/addon/fold/foldcode.js"></script>