* Add weakref parameter to attr.s()
#325
* Add weakref to simple_classes() strategy
* Rename changelog file with actual PR (420.change.rst)
* Add test_weakref_does_not_add_a_field()
* Add docstrings to new weakref tests
* Add missing blank line
* Correct weakref handling of __weakref__ attributes or an inherrited slot
* Correct typos and terms
* Rename to weakref_slot
* Parametrize more tests against weakref_slot True/False to expose trouble
* Check if __weakref__ has been inherited via a __dict__
* Correct copy/pasted comment
* Change weakref_slot default to True
* Tidy and correct weakref -> weakref_slot
Anders Huss