single file output

This is an attempt at fixing #17 
The main trick is to inject your own file loader. All files have to be collected first because dependency resolution might need them in a different order.

I had to copy a lot of code, but I'm not sure yet how best to refactor traceur in order to provide all necessary hooking points. Also, I need this to work now...

Things like error handling, source maps, and streaming support need more work.