Replace singular itype::use functors with a vector of iuse functors.
Check for particular iuse methods based on label instead of having function pointers everywhere.
Clean up some includes.
Add string-based stat modification methods to creature and player for easier procedural stat modification.
Add a new iuse_actor that encapsulates taking a drug.
Replace dedicated crack iuse with consume_drug definition.
Replace painkiller iuse with consume_drug definitions.