better libs for markdown demo

[Leon Sorokin]

First off, great project! While playing around with it, I noticed you're using to-markdown and showdown for the markdown demo. If you're interested in converting less trivial structures and/or GFM and markdown-extra support, please have a look at these libs.

https://github.com/leeoniya/reMarked.js
https://github.com/chjj/marked

cheers!
leon