Add ESP32-S2 MQTT Compatibility

This release:

• #63 Adds support for using the ESP32-S2 to the Adafruit IO MQTT API.
  • Adds usage example for ESP32-S2: https://github.com/adafruit/Adafruit_CircuitPython_AdafruitIO/blob/master/examples/adafruit_io_mqtt/adafruit_io_simpletest_esp32s2.py

To use in CircuitPython, simply install the Adafruit CircuitPython bundle.

To use in CPython, pip3 install adafruit-circuitpython-adafruitio.

Read the docs for info on how to use it.