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/boards.py

@@ -258,7 +258,7 @@ class LEDBoard(LEDCollection):
             on_time, off_time, fade_in_time, fade_out_time, n, background
         )
 
-    def _blink_device(self, on_time, off_time, fade_in_time, fade_out_time, n, fps=50):
+    def _blink_device(self, on_time, off_time, fade_in_time, fade_out_time, n, fps=25):
         sequence = []
         if fade_in_time > 0:
             sequence += [