Adapt to OPL3DUO (serial control OPL3 actual hardware)

[denjhang]

https://github.com/DhrBaksteen/ArduinoOPL2/blob/master/examples/OPL3Duo/SerialPassthrough/SerialPassthrough.ino
https://github.com/DhrBaksteen/ArduinoOPL2/blob/master/examples/OPL2AudioBoard/SerialPassthrough/SerialPassthrough.ino

Currently I use SerialPassthrough.ino of OPL3DUO, compile these codes with arduino and upload them to arduino nano.
After that I use dosbox-x and specify the port number (like com3) and I can use the actual opl3 hardware.

[Wohlstand]

This project isn't so active and it got into a very long hiatus (It doesn't have any significant updates after 2014, except for small bug fixes, the tool's UI tweaks, etc). I may suggest the libADLMIDI, the majorly reworked version of adlmidi turned into the library.