Upgrade to latest traceur

Fixes #16

This is basically a rewrite of ./compile.js that instead delegates to traceur's own compile function, plus a few test tweaks to make it pass. Since more of the ES6 features now requires the $traceurRuntime global to be included in the bundle to work, I've just included it in all bundles generated in `./test/bundle.js`. We could split this in two different tests, one that runs examples that requires the runtime, and one that runs examples that can live without the runtime. Not sure if it is really important though.

My goal here was to make as few changes as possible to and still make the test suite pass with an up-to-date traceur, I haven't really thought too much about the configuration options passed on to the compiler, like `{modules: 'commonjs'}` etc.

It would be nice to have tests for more of the es6 features enabled by the updated traceur, I've included one for class syntax, guess the rest is up for grabs.