OPNA FMGen changelog since adding into libOPNMIDI

- Shift-Jis to UTF8
- compiler optimize flags
- Added soft-panning to simulate full-panning when chip itself can do 3-state panning only
- fixed warnings and Windows builds
- fixed some mistakes in the code
- fixed C++98 compatibility
- Attempted to fix the SSG-EG behavior

The detailed changelog can be seen here:
https://github.com/Wohlstand/libOPNMIDI/commits/master/src/chips/np2

