Idea: Reuse compiled selectors

[Stranger6667]

Right CSS is re-parsed every time a new document is processed. Alternatively, there could be an API that will accept some CSS to build reusable inlining rules and then provide a way to apply inlining to new documents without re-parsing their CSS (meaning from style tags and remote stylesheets).

Additionally, it will be nice to compile CSS rules in the way they store ancestor hashes for fast-rejection.