Refactored PlayerSprite and EnemySprite classes to have a shared
CreatureSprite base class.

More work still needed to finish cleaning up CreatureSprite.

Part of #40
Began refactoring by removing unused function arguments and and unneeded
member variables

Part of #40
More refactoring of creature.py as prep for #40
More refactoring for movement. FPS is now 30, but the player can only
move every 10.

Part of #40
Re-added enemy movement. Finalized refactoring of Player and Enemy
classes.

Part of #40
Renamed movement.py to main.py and pulled code into a main function
Merge pull request #48 from nhandler/char-heirarchy

Char heirarchy