Generate classes from .idl files

DO NOT MERGE YET. I broke Karma and can't get it to come back to life due to subtle complications involving https://github.com/karma-runner/karma-traceur-preprocessor/pull/4 plus also RequireJS's horribleness as a packaging target. (I have an idea to fix it though...) Also I might want to figure out what to do with scripts/traceur-runner.js per the TODO left in there.

But anyway, this did shape up nicely.
This is not time critical but an early return would allow you to skip array allocation and more.