Pets regenerate over time

[Rad586]

Might conflict with vanilla design.
Make pets(or mobs in a list, for better compability) regenerate over time.

Sometimes we don't have fishes for cats, seeds for parrots, or we're just busy fighting enemies. Some modded pets can only be healed by potions. Our beloved pets may die from fire damage, drown damage or falling damage, it gets even worse if they are already in low health. Self-regenerating pets frees us from taking too much care of pets, and makes them more reliable.