Update 00.11

Update v00.11 changes:

• Fixed moving platforms adding their velocity to the player.
• Replaced 3 spike tile with 6 spikes. These cannot be traversed through.
• Tweaked level generation to combat some impossible levels.
• Added screen shake to camera on death.
• Added difficulty increase mechanic. Easiest at the start, hardest at 400 (above which, the difficulty is static).
• Added some test character skins.