Added ToC support

- added `markdown-it-toc-and-anchor` into the project
- integrated it, create a table of contents every in a markup by adding
`@[TOC]`

browser/lib/markdown.js

@@ -1,6 +1,7 @@
 import markdownit from 'markdown-it'
 import emoji from 'markdown-it-emoji'
 import math from '@rokt33r/markdown-it-math'
+import tocAndAnchor from "markdown-it-toc-and-anchor"
 import _ from 'lodash'
 
 const katex = window.katex
@@ -36,6 +37,9 @@ var md = markdownit({
 md.use(emoji, {
   shortcuts: {}
 })
+md.use(tocAndAnchor, {
+  anchorLink: false
+})
 md.use(math, {
   inlineRenderer: function (str) {
     let output = ''