Bugs
* Fix error of partial rendering, when an object is sideways in front of the player, next to a wall on the same side

Open Issues
* teleporters and spinners cannot be removed/enabled
* interaction can only affect one cell    
* The monster might also hit the player when the player choses to retreat (0 and 1 on D8).
* Roll initiative for the first attack (use upper bits of timer?)
* rework level layout for more fun

Fixed Issues
+ opening doors doesn't consume a key
+ doors open without a key
+ the fountain doesn't work (victory item not given)
+ double gates are rendered from all directions (entry of great hall)
+ switch is rendered from all directions (great hall)
+ Amulet of True Sight doesn't work anymore
+ non wall items are only rendered in the center line of view, 
  requiring architectural measures to prevent the player from noticing too easily
+ objects on adjacent squares are not rendered correctly (too close to center)
+ fixed broken death bitmap (due to vertical adressing mode)
+ death animation is broken
+ code doesn't fit into ATTiny85 anymore, need to optimize SSD1306 initialization
+ integrate Daniel C's fast OLED driver
+ Potion's healing effect applies immediately now

