More convenient playback

[ssfrr]

I'm splitting out the various discussions from #29 so they're easier to keep track of separately.

My plan has been to revive my old AudioIO package (just re-using the name) to be a metapackage that would export play and record functions, and auto-choose the audio backend (usually PortAudio, but WAV.jl has a native PulseAudio backend that doesn't require a binary dependency that I'd like to pull out as a separate package).

from @haberdashPI

I definitely see my current solution for this as a sort of band-aid rather than a good general purpose solution. I like the interface of just being able to call play or record, but yeah, ultimately it makes more sense to be able to switch out backends, with an implied default backend.