Arduino OPL2 v1.5.2

Two new examples have been added:

1. Scale - A demonstration on how to play notes
2. PianoBoard - Turn your OPL2 Board and Piano Board into a piano!
   • Sketch requires the Piano Board from Cheerful Electronic: https://www.tindie.com/products/cheerful/arduino-piano-board-2/
   • Sketch requires the Arduino Piano Board library to be installed: https://github.com/DhrBaksteen/ArduinoPianoBoard