Warning: this piggybacks on 'alt' text and can be broken if a manual alt text was specified on a <math> bit. Needs to be more nativey.
Also cleaned up the conditional setup code since we're already only called when a <math> is present.
* Pulled in MathJax 1.1 (minus the 112 megabytes of PNG "fonts")
* Pulled in some of <https://en.wikipedia.org/wiki/User:Nageh/mathJax> bits for initialization
This doesn't currently override PNG images, but does replace the text-form if you configure it.