Added support for embedded rulesets. Resolves #336.

Implements feature requested in #336. (Sorry for the trailing-whitespace changes. I have vim set to nuke those.)

**Update:** For posterity, this pull request adds the ability to override csslint rules on a per-file basis by embedding the rules in a special comment. It follows the jslint and jshint convention in style and meaning (defaults to warn, false is ignore, true is error).

``` css
/*csslint adjoining-classes:false, box-sizing:false, universal-selector:true */
```