Mercenaries should have a way to heal over time

[BillBeckerAtBounteous]

Unlike tames which can be fed to heal them, I could not find a way to heal (fairly expensive level 4) mercenaries who took a lot of damage. It would be nice if there were a way to give them healing potions, have them heal while under the umbrella of a ward or simply slowly heal over the course of time.

[jpw1991]

In Cheb's Necromancy, I recently implemented a Skeleton Priest that is able to heal nearby undead minions. We could do a similar approach here, but I prefer some of your ideas like the ward or slow regeneration over time.