Support option modem "speaker" (WAV file playback) control via ATM1 (turn on)

Support optional WAV files via .ini keys:
RingSound
ConnectSound
DisconnectSound

ATM0 turns "speaker" (WAV playback) off (the default), ATM1 turns on.

Ignore ATLn (speaker level), ATT (tone) and ATP (pulse) commands. These are
sometimes found in init strings which we don't want to prematurely fail with
a parse failure and "ERROR" result.

Increment version number to 0.2.