#sensorupgrade

For a while, we've had a SAMD09-based soil sensor (https://www.adafruit.com/product/4026) that uses the built-in capacitive sensing. It works well but has some non-linearity in its response to wet soil. We wanted to try a different system of measuring capacitance and update it to a 3~5V friendly ATtiny816 (https://www.adafruit.com/product/5681), which lets us ditch the regulator and shifting circuitry. We'll also Stemma QT-ify it and add a NeoPixel and an AHT20 low-cost temperature/humidity sensor (https://www.adafruit.com/product/4566) for an 'all in one' gardening sensor. The un-rendered part in the center is a 3-pin DIP switch in 1.27mm pitch, for easily setting the I2C address. Coming soon.