the game (backscrolling)
[H] Tux should fall while walking in tiles that have a space between.
+[M] Save score on per-level basis to make high-score
+[M] Save time on per-level basis to make low-time-score
+[M] Add bonus score for extra time left when finishing a level
[M] When aborting a level, lives and score should remain the same as they
were before. Solution: make more dependency between the game engine and worldmap
or just backup those variables before starting a level. - fixed?