Spaces before combinators (>, +, ~) shouldn't be required in CSS selectors

Created by: abotalov

Currently the following produces an exception:

Oga::CSS::Parser.parse_with_cache('body>p')

I think it shouldn't. See combinator grammar at http://www.w3.org/TR/css3-selectors/#w3cselgrammar and http://www.w3.org/TR/css3-selectors/#selector-syntax ("White space may appear between a combinator and the simple selectors around it.")

Also the spec has some examples where whitespace doesn't appear before combinator.