Make noises on Ubuntu 18.04 with Pulseaudio

[teknico]

WIP, don't merge, contains ugly workarounds to #1. :-)

On Ubuntu 18.04 with Pulseaudio, the with_max_sample_rate method returns
Format { channels: 1, sample_rate: SampleRate(192_000), data_type: I16 }
but the code assumes:
Format { channels: 2, sample_rate: SampleRate(44_100), data_type: F32 }
so we hard-wire it.

Then cpal returns a buffer of length 8820, which is not a multiple of 64: the code tries to fill the too short tail and we get an index out of bounds panic. The workaround shown here is to not use the buffer tail. I also tried skipping the tail of the last worker chunk, but in both cases the resulting audio is scratchy, because the waveform gets cut off or has additional pauses.

I could not find a way to tell cpal to use a given buffer size, nor to tell the workers to use a different chunk size.