Feature Requests: Support for non-DFR key input, and Keypad Calibration

[LabRat3K]

Looking for feedback on whether these are areas you would want to see developed, or not.

GPIO keypad

I have coded up a simple "GPIO on/off" input in place of the DFR_Key module. I wasn't sure if this is a direction you wanted to take the project, or perhaps explicitly DIDN'T want to take the project. The first version was somewhat invasive, but the second is a drop in replacement for the DFR_Key keypad class. It could merge with master, or could be kept as a side branch for others that may not have access to a DFR keypad and still want to explore/tinker with the project.

See:dev-labrat-simple_gpio_input

Key Test & Calibration

Oh.. it also include a "Keypad Test" routine... which could then be the starting point for a "Keypad Calibrate" routine. I was thinking it could detect that it hasn't been initialized and then poll the user for each key press, recording the detected values in flash. If this is something you would like to see included, I can continue to develop it.