While we're on Chip-8, I updated my SMS-native emulator with the "new" roms.

There's a problem. Some of the Chip-8 docs specify that the RND opcode should set the specified register to a random number less than or equal to the byte operand. However, this is wrong; it should set it to a random number ANDed with the operand, according to older docs from the HP-48 days. This is certainly a lot simpler to achieve on a simple CPU.

The former is needed for "rocket.ch8"; the latter is needed for "Tetris", otherwise it bugs out all over the place.

The fix I'm using is to edit "rocket.ch8"; change $20 to $1f at offset $49 and $40 to $3f at $4b.