browserify coffeescripts

This branch adds browserify support to terraform's coffeescript compilation step. I've added tests and created a sample app to demo the behavior: https://github.com/zeke/harp-browserify-test

It would be ideal to also browserify regular old `.js` files too, but it wasn't immediately clear to me how to do that. Happy to make amendments to this PR with some guidance. :)

cc @sintaxi @michael-lawrence @kennethormandy @kevinsimper, because you all participated on https://github.com/sintaxi/harp/issues/55

PS I didn't revamp the `package.json` formatting on purpose. I think `npm` is doing that automatically.