#124 low-latency pulseaudio pipeline using --input-buffer

[Raphaël]

https://github.com/chirlu/sox/pull/4

sox -t pulseaudio depends upon pulseaudio buffering.
By default buffer size computation leads to (very) significant latencies (up to 2 sec)
A confidential solution for the happy fews is to rely on the PULSE_LATENCY_MSEC environment variable.

This commit publicly exposes pulseaudio in/out buffers by binding them to sox --[input]-buffer options.
With sox --input-buffer=40000 -t pulseaudio default -t pulseaudio default you now get a low-latency pipeline.

Notes:

• Since --input-buffer defaults to 0, the default (high-latency) behavior stays unchanged
  (if PULSE_LATENCY_MSEC isn't set)

• Since --buffer default to 8192 and can't be set to 0, it'll now have priority over
  PULSE_LATENCY_MSEC (for the playback stream)

[Raphaël]

ping?