mpatch: remove dependency on Python.h in mpatch.c Now all the CPython-related stuff are referenced only from mpatch_module.c with mpatch.c being freely usable from a future cffi module

mpatch: split mpatch into two files

mpatch: provide things that will be exported later with a prefixed name For cffi a bunch of mpatch functions need to be visible through a .h file. This change renames them so it won't create potential c namespace conflicts.

mpatch: change Py_ssize_t to ssize_t in places that will be later copied