+ * tux always jumps to full height at the moment - ok
+ * invisble blocks are visible and make the game crash when bumped - ok
+ * reimplement spikes as objects - ok
+ * what to do when stuck under tiles (after using duck-sliding)
+ * do we want multi hit scores again?
+ * tux doesn't stop at igloo anymore
+ * background particle systems are too slow - ok
+ * buttjump is deactivated