Neo Trinkey -- Capacitive touch pad support

[lynnpepin]

Per [https://github.com//pull/471], the Adafruit Neopixel Trinkey support was merged in without support for the capacitive touch buttons.

I'm happily using neo_trinkey without it :) But I am personally looking for such support.

I would actually love to take this on myself. I'm a novice in both Rust and embedded, and I've scoured the existing Rust and CircuitPython source but I'm a bit lost. If anyone has any pointers or recommendations, I'd certainly appreciate it so I can poke at it during weekends :)

[sajattack]

there's more details on the peripheral touch controller in #420

[lynnpepin]

Checking it out-- thank you!