get_events should really return a list of events
Naming things in a more meaningful way.

- We are focusing on getting the world update cycle right; variables and
  methods have renamed to reflect this fact.
Let user class provide methods to handle itself
Implement the event system.

- Very very rough.  Just making it a callable object that will execute
  the intended action at where the event queue is processed.
Integrate the use of events into the core engine

- Make sure that certain actions will ensure an event is created.
- Also make sure the update world method process all the events that
  have happened.

(dodecanote: the core tests that were all passing before I ripped
everything apart once again passed).
Somewhat less pedantic way of handling time travel

- Attempts to travel back in time will no longer throw an exception, but
  rather assume to have taken place right after the last time the world
  was updated.
Merge https://github.com/metatoaster/IdleISS

Conflicts:
	tests/test_core.py