Merge pull request #17 from jusa/dev

Small convenience fixes and update README
[source] Set and keep IN_VOICE_CALL for voicecall source.

After AUDIO_DEVICE_IN_VOICE_CALL has been enabled for source, do not
switch to any other routing. This would break the recording. Changing
output routing changes input routing correctly to match the output route
(for example with earpiece output use internal mic for input, for
headset output use headset mic for input) as long as input has
AUDIO_DEVICE_IN_VOICE_CALL route.