Use external files for tests

[tonyganch]

As we test stylesheets, it seems rather strange to include css code inside js files.
It's hard to write and hard to find a certain case.

I'd love to have two files for a test, e.g. input-x.css and expected-x.css.
Configuration can be set inside test.js or as a separate file config-x.json, where x is test's id.

This would help to test large files and stylesheets with indent-based syntax.

[L0stSoul]

i think in the same way, i just use this way of testing for vendor-prefix-align option.
I think we need to code some utilites function for this.

[tonyganch]

Implemented a long time ago