AudioStream API

Hi @PaulStoffregen,

We're exploring adding an AudioStream API to Arduino that extends the current Stream type. The draft interface can be found here: [api/Audio/AudioStream.h](https://github.com/arduino/ArduinoCore-API/blob/master/api/Audio/AudioStream.h). We would appreciate any feedback you have on it.

We've taken a look at the Teensy Core's [AudioStream type](https://github.com/PaulStoffregen/cores/blob/master/teensy3/AudioStream.h) and noticed it doesn't have any public interfaces to access the raw sample data. Was this done for performance reasons?

Uses cases we are thinking about include:
- [reading a file from SD card and playing back via I2S or DAC](https://github.com/arduino/ArduinoCore-API/blob/master/api/Audio/examples/WaveToI2S/WaveToI2S.ino)
- [reading data from a I2S or ADC microphone and saving to SD card](https://github.com/arduino/ArduinoCore-API/blob/master/api/Audio/examples/I2SToWave/I2SToWave.ino)

Inizia leggendo api/Audio/AudioStream.h e gli esempi Audio WaveToI2S/WaveToI2S.ino e I2SToWave/I2SToWave.ino, quindi confronta il tipo AudioStream di Teensy collegato. L’issue chiede un feedback su un’interfaccia in bozza e sulle ragioni alla base di un design esistente, quindi per completarla sarebbe necessario concordare una direzione per l’API invece di apportare una modifica al codice chiaramente definita.

Scritto dal modello di indicizzazione a partire dal testo della issue.