added some new sprites, created a difficulty screen
merge master into level_selector
removed some delays from tweens. More snappy.
user can now choose difficulty. However it doesn't have an affect on the actual gameplay next.
input sensitivity now affects keyboard movement as well
difficulty levels now implemented. Hardcore is really fun.
fixed a bug where gameogre screen would show up twice due to collision detection.
added back buttons to all states
Merge pull request #17 from johnlok/level_selector

Level selector