lavd/pulse_audio_enc: add buffer fullness messages

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
lavd/avdevice: add volume messages

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
lavd/pulse_audio_enc: implement volume messages

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
lavd/pulse_audio_enc: implement pause messages

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>