Initial impl of handler

This creates a Handler JS object that can take callbacks that, if created from javascript, will then be called from C++.

Currently nothing is passed to the callback functions - they are just stubs. Next step is to actually pass back appropriate objects if this design makes sense.

Other tasks:

 - [x] - figure out why a hang happens if `console.log` is used within one of the callbacks. The hang appears to be because one thread is not releasing a lock while the main thread is waiting to release memory.

![screen shot 2013-10-02 at 12 53 41 pm](https://f.cloud.github.com/assets/20300/1256812/799c036c-2b9c-11e3-8b13-0315e53c0fc1.png)