Clarify which "identifiers" in the C API are macros

Documentation

The "Python/C API Reference Manual" is an excellent resource but could be even better
if C macros were marked as such.

For a programmer that writes directly in C it doesn't matter which identifiers are real C functions
and which are C macros. However, when Python is used through libpython only the
C functions are available. This is the case for languages embedding Python through ffilib.

As an example: Consider the C macro PyImport_ImportModuleEx and the C function PyImport_ImportModuleLevel. They are documented in a way that makes it impossible
to guess that one is a C macro.

PyObject *PyImport_ImportModuleEx(const char *name, PyObject *globals, PyObject *locals, PyObject *fromlist)

PyObject *PyImport_ImportModuleLevel(const char *name, PyObject *globals, PyObject *locals, PyObject *fromlist, int level)

A look in "Python.c" (or friends import.h here) will reveal that PyImport_ImportModuleEx is a C macro.
But it would be a quality of life-improvement, if a simple "C Macro" were added below the
signature of C macros.

This "C macro" annotation could have the same style as the "Return value is a new reference" annotation.
(maybe with a different color).

Python/C API Reference Manual から始め、文書化されている PyImport_ImportModuleEx と PyImport_ImportModuleLevel のエントリを比較します。import.h を調べてマクロの違いを確認し、既存の戻り値アノテーションがどのように生成されているかを特定します。C 関数を誤って分類することなく、API ドキュメント内で C マクロが明確に示されれば完了です。