support pure javascript

This pull requests adds support for generating pure JavaScript code instead of CoffeeScript code. It also removes the hard dependency on CoffeeScript, allowing Rails apps to make use of this gem without requiring CoffeeScript as a dependency. (For my own case, this also allows me to use a version of CoffeeScript that this project's `gemspec` would otherwise prohibit.)

The generators can produce pure JavaScript by explicitly passing  `--javascript`, or implicitly by simply omitting CoffeeScript from the `Gemfile`.

This pull request addresses #46. It also adds a pure JavaScript component to the demo.

It is thoroughly tested.