Setup package.json and clean up node_modules

Adding the `package.json` allows other projects to use `npm install --save git://github.com/Ezku/coffee-injector.git`. With this in place you could also publish this project to npm.

According to [npm's docs][1] `node_modules` shouldn't be committed for libraries, so I removed them (and `node-promise`).

[1]: https://npmjs.org/doc/faq.html#Should-I-check-my-node_modules-folder-into-git