Destroy the enemies! arrow and melee 

The code is not completely combat-ready, but I figure it's about time for a merge.
Press B for melee attack and SPACE for arrows.
 We can do a code review first if you prefer. As of right now the melee attack only works if the enemy is to the right. This shall be remedied shortly.

new-comers:
- getRoomPosition(), getRoom() methods in Entity class
- keyReleased(), keyPressed() methods in MainGameState
- Thugs now blink when attacked ( render() in Thug class)
- plenty of new fields in Hero (hero TOTALLY doesn't need ANY refactoring)
- major additions to checkAttack() within hero
- Arrow class
- I'm sure there's more that I can't think of