Add another level of nesting of CSS rules in tests
Refactor config options in module Rtlize
Add require 'rtlize/declaration' in rtlizer file
Return compatibility with ruby 1.8

Ruby 1.8's RegExp engine doesn't understand look-behind or named groups.
This commit gets rid of those features in the used regular expressions.
Refactor & rename some regexp expressions

* Refactor long RegExps into separate methods.
* Use more consistent names for RegExps.