Make tests work reliably on the Pi

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.

gpiozero/pins/mock.py

@@ -159,7 +159,7 @@ class MockPin(Pin):
         # that's about all we can reasonably expect in a non-realtime
         # environment on a Pi 1)
         for actual, expected in zip(self.states, expected_states):
-            assert isclose(actual.timestamp, expected[0], rel_tol=0.01, abs_tol=0.01)
+            assert isclose(actual.timestamp, expected[0], rel_tol=0.05, abs_tol=0.05)
             assert isclose(actual.state, expected[1])