Feature preprocessors

Hey Featurists!

I just made this neat `browserify` transformer able to handle `html` preprocessors such as `jade` or `handlebars`.

It requires the `browserify` to be ran programatically so the user can setup its preprocessor. See updated README for an example using `jade`.

This feature will also greatly ease the dev of things like `jade2js-browserify` by just wrapping this one with some configuration (I plan to do this one very soon).

Please tell me what you think ;)

Arnaud.