Compress option

[Andrew Abramov]

• Use csswring for compress by default: compress: true.
• Support native compressor: compress: 'native'.

[Nickolay Ilchenko]

After discussion, decided not to use the native stylus compressor, because he minified only .styl files and css remains as is because it not open this @import.
Decided to do this after rendering using clean-css