Selects 300 bps ASCII with V.21 mark/space freqs (channel No. 1) per
"ITU-T Recommendation V.21" https://www.itu.int/rec/T-REC-V.21-198811-I/en

Baudmode 'v.21' is equivalent to '300 --mark 980 --space 1180'.

Drop old comment refering to incorrect V.21 freqs.

Reported-by: jboone@github (thanks!)
GitHub: Fixes kamalmostafa/minimodem#42

Specifically, add new sndio backend to the end of the default backend
selection #if chain, restoring the previous default selection behavior.

Reported-by: baimafeima@github (thanks!)
GitHub: fixes kamalmostafa/minimodem#29

and fix all zeros output for "--binary-raw 64"

Reported-by: increa@github (thanks!)
GitHub: fixes kamalmostafa/minimodem#43

When program keeps running, the ### EOT message allows the user
to know that the stdin has been fully transmitted.

OS X doesn't provide md5sum.
https://github.com/kamalmostafa/minimodem/issues/24#issuecomment-213816836

Fixes: tests/17-verify-tx-consistent-float.test

This might also relate to:
https://github.com/kamalmostafa/minimodem/issues/24

PASS: 16-verify-tx-consistent.test
FAIL: 17-verify-tx-consistent-float.test

The FAIL is due inconsistency in the .wav header (only for floats)
constructed by libsndfile -- its different every wall-clock second.
Even just a bare header (no audio samples) shows the effect:

  minimodem --float-samples --tx 1000 -f /tmp/xx.wav </dev/null
  sum -r /tmp/xx.wav
  sleep 1
  minimodem --float-samples --tx 1000 -f /tmp/xx.wav </dev/null
  sum -r /tmp/xx.wav

This might also relate to:
https://github.com/kamalmostafa/minimodem/issues/24

For non-interactive output (writing to an audio file), generate the
idle output carrier for same duration that the input is idle.  Makes
this case generate an output .wav file of just over 1 second duration:

  { echo hello; sleep 1; echo world; } | minimodem --tx -f /tmp/xx.wav 300

Clean up the "emit idle tone" code, which should never have involved
tx_leader_bits_len (that was a copy-paste laziness).

"Emit idle tone" simply generates the idle tone for a hardcoded period
of time now codified as 'idle_tone_usec' and set to 1/25 of a second
(to match the existing behavior).

static analysis from clang scan-build detected some paths
in the call to fsk_frame_analyze where ampl_out is not being
set:

fsk.c:493:13: warning: Assigned value is garbage or undefined
            best_a = ampl_out;

..probably the sanest approach here is to initialize it to 0.0
just to avoid it being garbage rather than setting it to zero in
the failed error paths in fsk_frame_analyze.

Signed-off-by: Colin Ian King <colin.king@canonical.com>

Signed-off-by: Colin Ian King <colin.king@canonical.com>

Be more explicit with parenthesis to avoid any possibly confusion
about operator precendence.

Signed-off-by: Colin Ian King <colin.king@canonical.com>

Signed-off-by: Colin Ian King <colin.king@canonical.com>

Signed-off-by: Colin Ian King <colin.king@canonical.com>

Thanks to Colin Ian King <colin.king@canonical.com>.

Remove confusing old copy of README.