MPR121 support as a Capacitive touch, IO expander and PWM LED driver

[davetcc]

Discussed in #184

^{Originally posted by alextrical February 2, 2023}
MPR121 GPIO and LED Driver Function
I was wondering if it would be possible to get support for the MPR121 added to your library, as all the current implementations on Arduino only cover a fraction of the functionality of the device.
The chip has 12 Capacitive touch inputs, 8 of which can be used as GPIO or PWM generation for driving LED's

I would be happy to provide you with hardware (and/or donation) for testing if that would be of any assistance, as I believe this would be an amazing chip for the price for all the functionality it has to offer.

Once again thank you for your amazing work.