This is a quick *untested* implementation of a background threaded
queue for `MotionSensor`. The optional *queue_len* is the number of
values to store in the queue, *sample_rate* is the number of times per
second to query the motion sensor, and if *partial* is False (the
default) then the `motion_detected` property won't return anything until
the queue has been filled.
Expand gitignore to include the usual py developing stuff, add an
__init__ to make this a legitimate package, move GPIO initialization
into the package init, import all stuff from input and output devices in
the package to enable the access demonstrated in the example, remove a
duplicate method from LightSensor, and make motion_detected a property
(for consistency with is_active which it presumably parallels).
