Allow loading custom waveforms via sysex

[tstirrat]

Allow loading waveforms at runtime with SysEx messages

Note: Requires an ArduinoBoy patch that will pass SysEx through to the GB serial port.

• All 16 waveforms are now stored in SRAM
• The currently selected waveform in CH3 will be overwritten and will persist through reboots

Message format:

0xF0: Sysex
0x7D: Non commercial
0x69: Device ID - chosen arbitrarily, open to suggestions
0x02: Channel - always 2 here for the WAV channel (CH3)

... 16 bytes of wave data

0x7F: SysEx EOF

This loads into the currently active wav slot. Open to suggestions about targeting specific slots with the message payload.

	PR	Description
👉	#6	Allow loading custom waveforms via sysex