Add "heal" enricher (identical in function to "healing" enricher)

[roth-michael]

All other enrichers that have a corresponding activity match exactly the activity name (damage, save, check) - I'd say /healing should just become /heal but that'd break a good chunk of existing enrichers, so at the least it should have a deprecation period, at most simply keep both around and alias /healing to the "true" /heal.