Sorry! Dave's messing around with the pin implementations again.
Hopefully the last time. The pin_factory is now really a factory object
which can be asked to produce individual pins or pin-based interfaces
like SPI (which can be supported properly via pigpio).
Knew I'd missed some patches to the docs! This re-applies the
aforementioned doc patches and also fixes the last RGBLED example (which
was subtly incorrect in the original docs)
