docs: fix missing pin methods and improve docs

[microbit-matt-hillsdon]

• fix missing space in directive that caused methods to be omitted.
• recast the get_mode() return values as their Python values rather than C names which aren't defined in Python.
• remove duplicate class definition for MicroBitAnalogDigitalPin.

[microbit-matt-hillsdon]

get_mode return values taken from https://github.com/microbit-foundation/micropython-microbit-v2/blob/eba8995843ebc7246765b364710543c9ffee344a/src/codal_port/microbit_pinmode.c#L97