Traceur

@bcamper 

I think this is ready for review. 
A couple of things to note. 
- I tried to remove all `require` statements but there a few still. They should only be used when we have to do something dynamic.  
- I have not started using the class syntax yet because we would have to change the spacing on methods.  This will make any merges more difficult 

Let me know what you think. 

This is a misnomer now since the traceur runtime isn't worker-only, it's also included in the main thread bundle. We could create a new define called EXTERNAL_FILES or something for non-browserify files that need to be cat'ed onto the bundle (not the same as EXTERNAL_MODULES, since that is a browersify-specific option).