Merge branch 'main' of git.adrian.geek.nz:/srv/git/haskell-stylist into main

Tweak priority to be a list for the sake of cascadeLayers.

Improve documentation, release version 1.2

Rework psuedoelement infrastructure so they can be their own boxes.

Code cleanliness fixes.

Code cleanliness: Interpret Data.CSS.Style.Importance.splitProperties return value correctly.

Test/fix cascade logic for selector specificity.

Draft alternate API.