Updates the module to work on v12. Closes #8, #10, & #14
Removes half-level proficiency support for PCs. Fixing the issue with the level adjustment applying to untrained skills was non-trivial.
If you want to handle half-level proficiency for PCs use the following rule element on an effect/feat on the PC.
{"key":"AdjustModifier","selector":"all","slug":"proficiency","mode":"subtract","value":1,"predicate":[{"not":"proficiency:untrained"}]}