Adding option to disable CSSParser validator

Allowing the user to disable the CSSParser validator that [`cssutils.parseString`](http://pythonhosted.org/cssutils/docs/parse.html#parsestring) uses. This adds an optional argument that allows the parser to inline unsupported attributes and values.

``` css
.example-1 {
  fo: bar;
}
.example-2 {
  color: baz;
}
```