Add pin_factory to all relevant class docs

Also tell a whole load of lies about what's a keyword-only arg. In the
vast majority of cases, pin_factory (and other args) *aren't*
keyword-only ... but we'd really like them to be, it's just difficult
while maintaining py2 compatibility.

gpiozero/boards.py

@@ -961,7 +961,7 @@ class StatusBoard(CompositeOutputDevice):
         super(StatusBoard, self).__init__(
             _order=labels, pin_factory=pin_factory, **{
                 label: CompositeOutputDevice(
-                    button=Button(button),
+                    button=Button(button, pin_factory=pin_factory),
                     lights=LEDBoard(
                         red=red, green=green, _order=('red', 'green'),
                         pin_factory=pin_factory, **kwargs