Native CoffeeScript support

I was trying to package a CoffeeScript library for browser support using your awesome browserify CLI.

Due to nested module dependencies, I wasn't able to use coffeeify because I do not know what modules are required by each CoffeeScript module and given the work you've already done, it was more easy to add natively (when module-deps encounters a .coffee file, it just compiles it and hands it off).

It you accept this pull request, there is corresponding one on node-resolve (https://github.com/substack/node-resolve/pull/23) to also accept.

Cheers!