New enum Animal_action - actions to take when we encounter an animal.  Lookup/name functions for Animal_action.  Include a default Animal_action in Animal_datum, as well as a chance to flee.
Data for default actions and flee chance.
int Building::hunter_level, the only hunting camp-related value in Building, tracks the combat level of our hunters (to be compared to animals' danger value).
Player_city holds an Animal_action for each Animal, for hunting camps.
New Race_skill SKILL_HUNTING, for hunting camps.
Hunting difficulty data for Terrain_datum.