Record audio input from the user microphone, export to .wav or ArrayBuffer
AudioRecorder has 2 public methods : startRecording() and stopRecording(format, filename,
callback)
startRecording is synchronous and doesnt take any arguments.
stopRecording format argument accept 2 formats : 'wav' or 'Uint8Array', the first one
must be
called synchonously, the second one is async.
