NEW: converters/unsf

Hi ports --

Attached is a new port, converters/unsf. UnSF is a tool to convert
SoundFont sf2 files into GUS patchesets.

This is the program I used to create the TimGM6mb patchset for Timidity
(see my previous email about that).

---
pkg/DESCR:
UnSF is a tool to convert SoundFont (sf2) files into GUS patches.
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OK?

~Brian