Adding module export support outside of stomp.coffee

I noticed on #88 that you had desired for the module exports to be outside of the stomp.coffee. This is a very breaking change as I did that and would require a major version bump. However, I added the ability to also export as an AMD module. There is some other cleanup as well. Please let me know if you would like things changed or how you would like to proceed.

Thanks for this awesome project!