refactored map generation into a helper class
added tile-related helper methods to Map class

- removeEntity()
- isEmptyFloor()
  * modified getRandomFloorPosition() to use isEmptyFloor()
created Destructible and SimpleAttacker mixins
added attacking capabilities
fixed error in hasMixin()
fixed error in removeEntity()
methods for getting HP and HPmax
added new HUD class
implemented HUD status and message
removed logging message
messages clear after a given amount of time

- messages clear after aging for 10 turns of inactivity
made attack message more descriptive
reduced font size and increased canvas size
removed turn counter log message
include stats in Entity property hash