Additions:
-added some moody music to play in the background
-added methods pushRoom, popRoom, and clearRoomStack to Player

Changes:
-changed backCommand and player:walkTo to use Player pushRoom and popRoom
-changed xyzzyCommand to use Player clearRoomStack
-changed sleepCommand to use Player clearRoomStack
-fixed bug in Inventory init where points were not correctly added to the item
-changed Room so that exits is now public.  This was done so that the useCommand would have better access to modify room exits
-cave now initially list all exits  except up as dark.  This should help keep sneaky players from knowing which direction would be revealed when the lantern is used

TODO:
-add method(s) to Room so that exits can be removed