Always bind Cython functions in Py3 (GH-3683)
Always bind Cython functions in Py3 (GH-3683)

Rebased 1bb26b964060392ecb08c3b6c8ca4626e5c1eec7 for cython 0.29.x,
and made conditional to Python 3.  This does not solve the original staticmethod problem
in Python 2 but it does resolve classmethod problems in Python 3.9.  Therefore, it unbreaks
other packages on Python 3.9, improves overall state for Python 3 and does not introduce
regressions in Python 2.
scoder/cython,cython/cython,da-woods/cython,scoder/cython,da-woods/cython,da-woods/cython,cython/cython,scoder/cython,cython/cython,cython/cython,da-woods/cython,scoder/cython