Markdown updates + TeX math support

This one is a doozy. Replaced the markdown lib with Marked, which seems
to have good support, and also allows GSM (github). Works great, from
what I can tell.

Also implemented MathJax library which gives us TeX-style math. I'm not
super excited that it loads scripts dynamically, but it works great and
doesn't make any external requests/posts.

Updated "Formatting help" section in editor to show new equation
format examples.

Centralizing processing of all note body text through functions.js
(view::note_body()).
644 new libs
removing old markdownlib