Add "legend" to specify what instrument is playing on what channel
Rename OPL3 to OPL3IF to avoid collisions

It represents an interface to OPL3 cards, not the cards themselves.
Avoid collisions with the zdoom objects.
Import zdoom's OPL emulators

zdoom offers three OPL emulators.
See http://zdoom.org/wiki/OPL_synth_emulation
Make use of their object-oriented interface.
This implies switching to float samples.

Pick the CPU-heavy but accurate JavaOPL for now, but this needs to be
configurable using a command-line switch eventually.

Source files were imported from zdoom git commit b285cbe.
Implement full panning

This avoids the sudden jumps while panning in for example the Raptor
soundtrack.
Move the original dbopl to oplsynth

Needs to be integrated into the same interface as well; this is a
newer/better version than present in zdoom.
Integrate original dbopl as DBOPLv2
Simplify delay logic in midiplay

Count in samples instead of seconds.
Report audio underflows asynchonously

No more ugly printf() that nuke the interface.
Add ymf262.cpp OPL3 emulator from MAME/VGMplay
Add TODO to ymf262.c
Make OPL emulator and fullpan configurable on command line
Add comment that YM3812 is OPL2 thus not useful at the moment
Add readme file
If not in percussion use 18 lines per chip instead of 23
Properly recognize .mus files

Recognize them at least. They can't be played succesfully yet.
gen_adldata.cc: Simplify MidiInsName logic, add misc GM instruments

Also fix a typo surdu -> surdo
Add two more doom instrument banks

- 65: Freedoom (source: https://github.com/freedoom/freedoom/tree/master/lumps/genmidi,
   originally from OpenBSD OPL driver
   http://www.openbsd.org/cgi-bin/cvsweb/src/sys/dev/ic/Attic/oplinstrs.c?rev=1.3&content-type=text/x-cvsweb-markup)
- 66: Ultimate doom replacement (source: http://psg.mtu.edu/pub/idgames/utils/sound_edit/genmid01.zip)
  by Dan L'Ecuyer <dlecuyer@tbase.com>
Allow bank selection through MIDI if `-bs` is provided

This should usually only be enabled for adlseq, not when playing from
MIDI files.