Prepare to interpret functional pseudoclasses.

Improve documentation, release version 1.2

Rework psuedoelement infrastructure so they can be their own boxes.

Add support for psuedoelements/classes.

Code cleanliness fixes.

Improve code cleanliness to avoid future bugs.

Data.CSS.Style.Selector.Index: fix potential crash.

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

Draft alternate API.