latex plugin revamp

This update addresses the two issues I was asked about the most:

 1. It now plays nicely with the typogrify library
 2. It works without needing to alter the template

In addition, this library has been totally overhauled and also does the following:
 * Correctly renders summaries, with logic to repair latex that has been cut off by the summary
 * Allows the user many more options to control how mathjax renders latex (see Readme)