Updated this to use a Survivor player instead of an Entity player, since Entity became abstract.
Added a getEntities() method that returns a Collection of Entities on the map to iterate through. Changed getEntity()'s parameters from two integers to a Location.
Added directionTo() and isAdjacentTo() helper methods.
Added render() and update() methods. The update() method currently handles moving. Also set the default Direction to Direction.SOUTH and changed setHealth() to a simple field setter.
Moved MainGameState's survivor rendering code to here.
Updated to support recent Entity changes.
Merge pull request #7 from mfrancis95/mike

Entity rendering and updating