...
added .id to unit.
added .container to unit, changed Squad accordingly.
Added get_delta to clock.
Made create_world.py less destructive.
Changed Stronghold.units to a Mapping, added factories, added functions for moving units in
and out of containers.
Cleaned up some buggy stuff in world.py
feed_units, bury_unit, imbue_weapon, split_weapon, imbue_unit, and a bunch of other stuff.