Loading MathJax in a hook

Created a demo for this in /examples/mathml.html

Looks like MathJax comes with a lot of assets! Is this something that I should clean up before we merge it?

@fchasen I merged from master and it looked like you also added the properties fix to parser.js and thus there was a conflict there that I had to delete a few lines to resolve. After merging back master everything seems to be fine.