Development: v0.1.6 - Fixed death powerup loop bug

  Death / Genocide / Black powerup now hits all squares for 1 damage.
Development: v0.1.6 - Difficulty tweaks and drawing changes

  * Increased difficulty slightly
  * Changed outline colour of powerups
  * Changed draw order to draw powerups before squares, bullets, player.
Development: v0.1.6 - updated Square "pathfinding"