Add Math polyfill

This implements the new ES6 Math functions.

The implementation is based on V8 and MDN as well as the spec.

The tests are mostly just smoke tests. I'm not testing a lot of
edge cases.
Can we have a comment to explain this one? This code is supposed to run the file as an end-user would run it rather than in the environment incidentally populated with Traceur things.  By adding `Float32Array` we are injecting traceur stuff and that's surprising to me.