Drop the runtime dependency on CoffeeScript.

* Move all source code from `lib` over to `src`.
* Adds a `prepublish` script to `package.json` that compiles all
  CoffeeScript files from the `src` to the `lib` folder.
* Add `src` and `vows` folders to `.npmignore`.
* Add `lib` folder to `.gitignore`.

Tests continue to use the CoffeeScript sources, to ensure that always the latest code is tested.

Fixes #11.