Add new support APIs to Stylist Traits, releasing v0.1.2!

Expose pseudoelements to PropertyParsers.
Add utility for parsing unordered shorthands.

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

Expose & fix treeFind/treeFlattenAll utilities.

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

Revamp XML-Conduit-Stylist API to avoid hard-dependency on Haskell Stylist.

Add utils for implementing :target-within, ensure unlayered styles take precedance.

Fix @layer to play nicely with the conditional at-rules.

If you're not using that, its still integrated into core.
Since the @layer rules are stripped by ConditionalStyles this shouldn't make a difference.

Extract parser, datatypes, & traits into separate decoupling hackage.