make Util.NO_DIRECTION a positive constant

clears warning
Merge branch 'master' of github.com:jlowdermilk/asylum-escape-game
Merge branch 'master' of github.com:jlowdermilk/asylum-escape-game
cleanup spritesheets
Merge branch 'master' of github.com:jlowdermilk/asylum-escape-game