Fix function signature casts in PyMethodDef structs that lead to warnings in gcc-8 (and actually make use of the warnings in gcc-8).
Fix function signature casts in PyMethodDef structs that lead to warnings in gcc-8 (and actually make use of the warnings in gcc-8).

da-woods/cython,cython/cython,da-woods/cython,scoder/cython,scoder/cython,scoder/cython,da-woods/cython,scoder/cython,cython/cython,cython/cython,cython/cython,da-woods/cython