Add "AudioInputAnalog" to the Audio Adafruit Fork

[FondsofFall]

I apologize if I might not be clear what it needs to be added as request. The library is missing AudioInputAnalog in audio.h (ported from Paul Stoffregen). The purpose to use as audio input on STEMMA port for ADC. I was trying to use Adafruit Microphone Amplifier breakout so I can use directly on Neotrellis M4 board instead of use headphone with built-in microphone only. If that is not possible , please let me know. Thanks.