Add worker-based syntax checking for Python

![](http://f.cl.ly/items/2Y3N093F0O1p3i2g2C20/Screen%20Shot%202012-12-27%20at%2017.44.46.png)

This uses [empythoned](https://github.com/replit/empythoned/) which is CPython compiled to JS using emscripten.
I realize the file size and the amount of JS is scary, ~5mb huge! But:
* This loads async.
* Loads in a worker.
* Gzipped ~800KB.
* Tested and works on all browsers with workers.
* Battle tested on repl.it and a couple of other web apps.

I want to use it on [Codecademy](http://codecademy.com), [repl.it](http://repl.it), and other projects.

_Other options could be https://github.com/bnmnetp/skulpt but I doubt the parser is fully implemented._