shared-bindings: Update DigitalIO.pull docs and validate that third (#188)
shared-bindings: Update DigitalIO.pull docs and validate that third (#188)

state is None and not anything.

Fixes #187
adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython