Add bower.json

Bower allows easy installation of front-end dependencies. By adding a
`bower.json`, your package is easier to discover and to install, because the
`main` property can provide a hint of where to find the main file of your
project.

You can install RGBaster with `bower install rgbaster`.

Two additional notes:

- You haven't provided any licensing information which means that no-one can use your library without your consent at the moment.
- It would be very helpful if you could tag your library with [semantic versioning](http://semver.org) so people can pin the library to a specific version.