Audio input API extension

[rzumer]

Some platforms support microphone input devices, the most well-known being the original Famicom controller. Emulators currently handle it via button presses, but true audio input could be made available through the API, which would allow emulators to at least implement some basic processing without having to handle capture themselves.

My initial thought is to simply provide raw audio frames with metadata (number of channels, frequency range, depth, etc.). Alternatively, resample/normalize input and provide data in a simpler representation, e.g. amplitude mean and extrema for each frame. I would like to open a discussion with this issue.

<Autechre> if we do add it hough
<Autechre> it has to become a Privacy feature
<Autechre> that people have to give permission to

[gouchi]

@rzumer This PR should help.