Define more SGB constants #71
Description
These are relevant to the Game Boy because of command transfer to the SNES, as described in https://gbdev.io/pandocs/SGB_Command_Packet.html.
Significant values for rJOYP:
- Initiate command transfer:
%00000000 - Send 1 bit:
%00010000 - Send 0 bit:
%00100000 - After bit transfer:
%00110000