v4

Version 4 (2023-04)

• Support protocol verfsion 2.2.
• Support READ_BOARD_INFO command.
• No longer set board versions and extra info (display type) at
  compiletime, but read them from board info from flash at runtime.
  This means that instead of producing a hex file for each board
  version, just a hex file per hardware type (interface board & hopper
  board) is produced that will be combined with a board info block at
  flash time.
• Removed version number block from flash.
• Size optimizations to make things fit on the attiny.