Added cooldown_hit to statblock, prevents players & enemies from being stunlocked due to fast/consecutive hits pushing them into the on hit animation.

Previously a problem existed where it was possible to become surrounded by enemies and if their hits lined up they would lock you into the "on hit" animation. I've fixed this problem by introducing a configurable cooldown timer on the "on hit" animation. This logic is also rolled into Enemy as well, which may affect the balance of the experimental minions patch somebody else is working on. I feel it affects it in a positive manner, however, as minions were previously overpowered because of this animation stunlock.

Code is up here for review.
Joseph (Ninwa on IRC)