Consider a mechanism for supporting 3rd party plugins

A great part of Rework/Styl is being able to extend it through plugins. While this is possible programically you can't use the same method from the command line.

This would allow you to specify plugins to use in a file. That gives you an easy spot to edit them and allows you to manage them in version control. Being a Javascript file, it also allows you a place to initialize and configure them.