Gotham font for blocks.
WIP for artist skin.

Now moves the avatar based on Turtle.x and Turtle.y. TODO: Make the skin to be set dynamically. Make the avatar show based on direction.

Set the zombie to face based on the direction.
Made Turtle skinable. The avatar images in artist and artist_zombie are just place holders.
Clean up.
Factored out common logic in loading Maze and Turtle skins.
Merge branch 'master' into turtle_skin
Moved load skin in Maze as a separate module.
Merge pull request #190 from nanan9177/turtle_skin

Turtle skin