Add support for RP2040/PicoW

[brentru]

Adds support for the Raspberry Pi Pico W and RP2040 boards supported by the earlephilhower/arduino-pico core.

Resolves #157

Test Sketch, adafruitio_02_pubsub.ino:

15:37:09.266 -> Connecting to Adafruit IO
15:37:20.366 -> Connecting
15:37:20.366 -> ..............
15:37:29.295 -> Adafruit IO connected.
15:37:29.400 -> sending -> 0
15:37:29.508 -> received <- 0
15:37:34.519 -> sending -> 1
15:37:34.553 -> received <- 1
15:37:39.588 -> sending -> 2
15:37:39.657 -> received <- 2
15:37:44.722 -> sending -> 3
15:37:44.760 -> received <- 3