spandsp: V.17 modem tests

spandsp 0.0.6

V.17 modem tests

# What does it do?

These tests test one way paths, as V.17 is a half-duplex modem. They allow either:

- A V.17 transmit modem to feed a V.17 receive modem through a telephone line model. BER testing is then used to evaluate performance under various line conditions. This is effective for testing the basic performance of the receive modem. It is also the only test mode provided for evaluating the transmit modem.
- A V.17 receive modem is used to decode V.17 audio, stored in a audio file. This is good way to evaluate performance with audio recorded from other models of modem, and with real world problematic telephone lines.

If the appropriate GUI environment exists, the tests are built such that a visual display of modem status is maintained.

# How is it used?