PEP7: Need to add a info "PyAPI_DATA() macro"

[bobozi-cmd]

When I read PEP7 and check Cpython source code, I found a deficiency that in https://www.python.org/dev/peps/pep-0007/#code-lay-out.
In this section, document said that

For external functions and variables, we always have a declaration in an appropriate header file in the "Include" directory, which uses the PyAPI_FUNC() macro, like this: PyAPI_FUNC(PyObject *) PyObject_Repr(PyObject *);

but when i check python 3.7.12+ and python 2.7.13, external variables actually uses the PyAPI_DATA() macro, like this:

PyAPI_DATA(PyTypeObject) PySuper_Type; /* built-in 'super' */

This may confuse beginners, could you please add this info in PEP7?

[brettcannon]

Please feel free to submit a PR, but people should not be reading PEP 7 on how to write C extension modules, just how to format C code for CPython's code base.