Gracefully Fail from Invalid Syntax

Running CSSPool against real-world poorly written syntax always results in errors like:
- parse error on value "}\n" (RBRACE)
- parse error on value ";" (SEMI)
- And selectors with ":not" return a 'parse error on value ":not(" (error)'

How do I make CSSPool just skip over the rule_set that it is having difficulties with? Thereby keeping all the valid CSS objects.

Thanks
