Added pathing, waiting.

The pathfinder and priorityqueueset modules are not mine; I took them
from Eli Bendersky's website
(http://eli.thegreenplace.net/2008/12/13/writing-a-game-in-python-with-pygame-part-i/)
straight out of his pygame tutorial. If I end up using their solution
for A* pathing, I'll throw them an email and make sure I ask permission
first, since I am pretty much just cribbing their code! For now, I just
wanted some fast and excellent A* pathing.

So, yes--enemies now go after the player. Also, you can spend a turn
doing nothing by hitting the '5' key.