Added an option for game refresh rate.
Added some new defaults. Better default typing.
Cleaned up main.py. Organizing constants/defaults.
Began implementation of the Player class
Initial commit of classes for managing the level
Added constants for vectors and other things.

Constants will be different than defaults, because they will not be changeable
by a player. The intention is that everything accessible in defaults.py will be
changeable by a menu option. However in constants, things like the direction UP
will always remain.