Ensure LEDCollection cleans up upon construction failure, rename some
internals to be a bit more obvious, rename PinGPIOUnsupported to
PinUnsupported, and some other stuff I've forgotten!
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).