Add hook for callers to run their own tests against attributes.

Parse namespace selectors.

Improve documentation, release version 1.2

Rework psuedoelement infrastructure so they can be their own boxes.

Test/fix parsing of psuedoclasses/elements.

Add support for psuedoelements/classes.

Improve code cleanliness to avoid future bugs.

Switch to new namespace for consistency with other modules like css-syntax.

Draft alternate API.