Barb: Remove berserk command and trigger via combat

[mikeclemson]

Remove berserk command. Remove berserk AFF flag as an equipment option. Barbarians with berserk learned will instead berserk in combat based on triggers, including blood letting (from one of barb's victims or from the barb himself/herself), low health of the barb (below 25%), or being victim to a damaging hit (25% of the barb's hitpoints). To keep it unpredictable, do not trigger on options like doing a lot of damage to an NPC (killing a weak mob in one hit should not trigger it) or getting a killing blow (also too easy/predictable).

[mikeclemson]

Perhaps drinking blood (from a severed head) would cause berserk. I really picture blood mattering for barbs, the sclera of the eyes turns blood red, pupil/iris a deep red hue.