This byte contains a checksum for the entire main game code. It is populated
by elite-checksum.py and is used by the encryption checks in elite-loader.asm
(see the CHK routine in the loader for more details).
.checksum0SKIP1\ This value is checked against the calculated checksum\ in part 5 of the loader in elite-loader.asm (or it\ would be if this weren't an unprotected version)