New features:
- added level 22 and 23
- On the welcome screen, the RESUME button now shows the next level to be played.

Bugfixes:
- the game no longer crashes when trying to resume a game beyond the last level
- fixed a bug that let attackers always appear as binary and never as hex
- MEM chips can now be sold

Miscellaneous:
- darkened some background images that were too distracting
- tapping on the CPU no longer pauses the game. (This was annoying on cluttered maps.)
