This implements the proposal discussed in the re-opened #279 to add a
pin_factory argument at the device level and remove the ability to
specify a pin instance to device constructors (they now only accept a
pin specification).
Note: there's still a couple of bits to tidy up (tests on "real" Pis,
and pin_factory.release_all needs refinement) but the test suite is now
at least capable of passing on a PC.
Factor out hardware SPI pin numbers; this is a effectively a rebase (and
minor modification) of @lurch's original patch which conflicted after
the merge of the remote-spi branch.
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).
