Release v0.9.1

__Don’t merge yet.__ Would like to have someone review how I’ve added consistent minifcation. This isn’t configurable, which I believe is the better approach here.

Includes new tests, which pass on Node 0.10.x on OS X 10.8.5 and Windows 8.1. I broke `npm install` on my Ubuntu VM, so if someone could test this there too, that’d be appreciated.

- Fixes #30 for HTML, CSS, and JS preprocessors