Add bower support

[jahvi]

It'd be awesome for dependency management

[thomaswelton]

The repo doesn't contain any build CSS files.
I use bower for my front end dependencies where the repo specifies a "main" array of files that should be included for use on the front end. I stopped using it for development dependencies like a compass extension.

Instead I use composer, which I'll be submitting a pull request for. You can see an example composer file here for a similar plugin. https://github.com/jlong/sass-twitter-bootstrap/blob/master/composer.json

[thomaswelton]

I've added instructions here #123 on how to install a fork of this repository using composer, and then generate a custom build of twitter bootstrap.