This is almost a straight copy'n'paste of picamera's development chapter
with a few minor changes to make it read sensibly for GPIO Zero; it
needs plenty more work to fulfil the goals of #451 but hopefully this'll
act as a reasonable base for people to work on.
While the tests work well on a PC or Travis, the Pi (where I ought to be
running them!) has some issues with the timing tests. Need to relax the
tolerance of the "assert_states_and_times" method to 0.05 seconds
otherwise it periodically fails even on something reasonably quick like
a Pi 2 (less failures on a Pi 3 but still occasionally).
Also reduced default fps to 25; if the default timing occasionally fails
on a Pi 2 it's evidently too fast for a Pi 1 and shouldn't be the
default; 25 also doesn't look any different to me on a pulsing LED.
There's also a bunch of miscellaneous fixes in here; last minute typos
and chart re-gens for the 1.2 release.
Also re-numbers energenie sockets 1-4 (as noted by @bennuttall in
comments to #239), and adds several "real pins" tests and board tests.
The bad-PWM stuff is currently disabled as it causes segfaults when
running the tests and I can't seem to trace the cause at the moment.
Finally, I've tweaked the deb config to suggest gpiozero, removed spidev
as a mandatory dep (which'll fix installs on wheezy for py3), and
there's some more miscellaneous last-minute stuff here that I can't
recall...
