markdown-it 介绍
markdown-it 是 Markdown 解析器，100% CommonMark 支持，易扩展，语法插件支持，速度非常快，默认保存。
简单示例
// node.js, "classic" way:
var MarkdownIt = require('markdown-it'),
md = new MarkdownIt();
var result = md.render('# markdown-it rulezz!');
// node.js, the same, but with sugar:
var md = require('markdown-it')();
var result = md.render('# markdown-it rulezz!');
// browser without AMD, added to "window" on script load
// Note, there is no dash in "markdownit".
var md = window.markdownit();
var result = md.render('# markdown-it rulezz!');