Separate out `:not()` selectors from CSS 2.1 selectors.

IE8 won't execute the CSS block if it contains a CSS3 selector.
This makes IE8 still execute the CSS, and CSS3-compliant browsers
can support the `:not()`.
wrap comments at 80 chars
fix dangling brace
Merge pull request #290 from tilomitra/261-fix

Separate out `:not()` selectors from CSS 2.1 selectors.
Update and tweak HISTORY.md
Bump version to v0.4.0
Bump version to PRE