[docs] 3.9 docs references missing functions from 2.x

https://docs.python.org/3/extending/extending.html#intermezzo-errors-and-exc... has sample code that fails to compile with the following error: spammodule.c:11:7: error: implicit declaration of function 'PyModule_Create' is invalid in C99 [-Werror,-Wimplicit-function-declaration] m = PyModule_Create(&spammodule); spammodule.c:22:22: error: implicit declaration of function 'Py_DecodeLocale' is invalid in C99 [-Werror,-Wimplicit-function-declaration] wchar_t *program = Py_DecodeLocale(argv[0], NULL); spammodule.c:29:38: error: use of undeclared identifier 'PyInit_spam' if (PyImport_AppendInittab("spam", PyInit_spam) == -1) {