On par with clean-css 1.0.12 - ability to turn off @import processing.
On par with clean-css 1.1.0.

* `--debug` switch for minification stats.
* full color name / hex shortening.
* support for `@import` with media queries.
* raise error on broken imports.
* proper CSS expressions handling.
* rebasing imported URLs.
* better code modularity.
* require node.js 0.8+.