Added characters.

We now have a character that can wander about and collide with the tiles. Control him with the arrow keys and space to jump.

There's still quite a bit to do, such as what happens when he goes off screen, adding UI elements for his score and lives, what happens when he dies, etc. I imagine some code at will work it's way up the class hierarchy and vice versa as well.

Basically, I wanted this commit done before I went away for two weeks, so I did.