Removed reference to Actor.

Was using isinstance(entity, Actor). Instead, now uses hasattr(entity,
'max_moves') to check if it has, well, moves.
Changed entity.destroy().

Now registers a CompoundCmd(LevelRemoveEntity).
Removed add_tool() function in Actor.

It was really only being used for testing purposes, so it was not worth
converting to a Command. Removed instead.
Adding docstrings.

Docstrings added to level.
More documentation, disambiguations.

Changed Level.get_all_entities_at and Level.get_all_entities to
Level.get_all_eids and Level.get_eids_at. Did *not* change the
implementation! Just the names.
Actor done. Did not require large changes.

Note that turn_begin() and turn_end() don't use Commands! This is because
turn_begin() and turn_end() do not change any data outside of the Actor
instance for which the function is called.

On the other hand, we lose the 'logging' functionality of the Command, so
maybe I'll come back and change it later, or subclass/rearrange Command
class hierarchy to put in something similar to the Record class. Right
now, though, I'm leaving it.
Split Sense.detect_entities, added is_active.

Added an is_active attribute to Sense. Sense.detect_entities() now checks
to see if it's active; if no, returns empty. If yes, defers actual sensing
to the subclass' _detect_entities() function.
Wrote a couple of tests for peace of mind.
Beginning on Behaviors.

Renamed the parameters in the Behavior functions, added docstrings.
Changed Behavior._on_execute_pay_cost to Command.
New Command, use moves, reshuffled class structure.

Command is now a superclass of CompoundCommand and all the fragments.

Also added a new command to command_fragments, EntityUseMoves. (Not
implemented as with all Command fragments).
New method: LevelView.get_entity_name(eid)

Again, the underlying algorithm just looks in all of the squares and
checks to see if it's in one of them. Not ideal, but, hey.

A better way would be to have a list/map, updated on insertion/removal
from the map.
The Behavior class is up-to-date.

Changed an outdated function call to a newer, supported version. Added a
function to LevelView: get_actor_current_moves(eid).