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.

docs/api_generic.rst

@@ -33,7 +33,7 @@ are represented in purple, while abstract classes are shaded lighter):
 Device
 ======
 
-.. autoclass:: Device
+.. autoclass:: Device(\*, pin_factory=None)
     :members: close, closed, value, is_active
 
 ValuesMixin