Add PulseAudio support to signal-estimator

[gavv]

signal-estimator is a command-line tool for measuring latency and glitches over audio devices. It's not part of Roc, but it was developed with our needs in mind.

Currently it supports only ALSA devices. We can use it to measure latency between roc-send and roc-recv command-line tools when they're used with ALSA.

Now we need to add PulseAudio support to signal-estimator. This will allow us to measure latency of our PulseAudio modules and command-line tools when they're used with PulseAudio.

See further details here: https://github.com/gavv/signal-estimator/issues/1