Todo
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+H: high priority
L: low priority
+[H] Scrolling is broken, should show at leats 3/4 of the screen to
+ Tuxs right, so that the player has a reasonably chance to see
+ enemies early on, currenty one can only not even a half screen ahead
[L] change lispreader to throw exceptions instead of simply assert() on
syntax error
[L] tux sometimes makes short jumps in the endsequence, mostly when