Update example, `temp_humidity.py`

This pull request updates temp_humidity.py:

Updates the example to use the "AHT20 Module - I2C Temperature and Humidity Sensor" instead of the DHT22 (discontinued on Adafruit's web store)
Updates the example to automatically create feeds, rather than the user manually creating them on Adafruit IO's frontend.
Adds a user-settable boolean for displaying and sending temperature data in either degrees Fahrenheit or degrees Celsius
- Resolves https://github.com/adafruit/Adafruit_IO_Python/issues/141

adafruit / Adafruit_IO_Python