One current thing: Cleanup mpg123_noise() ... remove that accidentally public symbol
or make it official. The functionality is in syn123 and it was never documented.

Things that need to be done...

... as always, mostly outdated.

0. Fix that ugly crash that happens sometimes when Ctrl+C-ing with jack output active:

Program terminated with signal 11, Segmentation fault.
[New process 6293]
[New process 6291]
[New process 6292]
[New process 6284]
#0  0x00002aced607695b in memcpy () from /lib/libc.so.6
(gdb) bt
#0  0x00002aced607695b in memcpy () from /lib/libc.so.6
#1  0x00002aced5b4f092 in jack_ringbuffer_read () from /usr/lib/libjack.so.0
#2  0x00000000004151dd in process_callback ()
#3  0x00002aced5b4bf40 in Jack::JackClient::Execute () from /usr/lib/libjack.so.0
#4  0x00002aced5b5f8da in Jack::JackPosixThread::ThreadHandler () from /usr/lib/libjack.so.0
#5  0x00002aced6354fa7 in start_thread () from /lib/libpthread.so.0
#6  0x00002aced60c802d in clone () from /lib/libc.so.6


1. mpg123 could pick up new sample rates suggested by the output modules (like a jack server fixed to 96kHz) and adapt to that.

Also, the libsyn123 resampler should be employed. Just generally, libsyn123
could also provide encoding conversions for formats not directly supported
by accelerated decoders. See out123, which is the 

2. What's about SINGLE_MIX?
Check what is _really_ happening there, make some test file...

3. Add playback of WAV files in mpg123 and out123.

Parsing the standard 44-byte header really is no big issue. WAV64 is
not really a thing, is it? Anyway, mpg123/out123 will probably just ignore
the length in the header. Also, both programs need a switch to enable
treating input as WAV, though out123 might get away with a default
mode of looking out for a header unless format options were given. Yes,
that makes sense. And perhaps I really should limit this to out123.

4. Enable some way to avoid libmpg123 messages (Note: …) messing up display
   of the progress bar.

- cleanup callback from app
- fprintf callback from app
- log buffer
