Serial Transfer to share High Scores in Part 2 #42

This lesson will introduce how to work with the 2 serial registers SB (0xff01) and SC (0xff02) in order to get a variety of multiplayer capability in the game.

1. Basic sending and receiving of a byte
2. Comms code considerations depending on if the current GB is master/slave, and how they would keep each other synced
3. Timeouts to ensure that the communication doesn't just hang

As a starting use case, this code should be used to add a very simple multiplayer feature to Part 2: share the saved high scores between different Game Boys.