engine.Zone:checkFilter: Added documentation, can set filter.allow_uniques to...

engine.Zone:checkFilter: Added documentation, can set filter.allow_uniques to allow unique items to pass the filter, special function takes the filter as its 2nd argument

engine.Zone:filterToString: updated -- handles subtables, functions, and other complex values

engine.Zone:makeEntity: the type parameter can be a list of entities

engine.Zone:makeEntityByName: Added documentation, type can be a string descriptor used to load a base list (follows makeEntity filter.base_list)

engine.Entity:resolve: Added documentation

engine.Birther: Bugfix: the order of resolvers is preserved when applying birth descriptors (causes resolver.attachtinker to fail with no equipment to attach to)