No longer export these 5 internal C API functions:
* _PyArena_AddPyObject()
* _PyArena_Free()
* _PyArena_Malloc()
* _PyArena_New()
* _Py_FatalRefcountErrorFunc()
Change comment style to "// comment" and add comment explaining why
other functions have to be exported.
Remove the pyarena.h header file with functions:
* PyArena_New()
* PyArena_Free()
* PyArena_Malloc()
* PyArena_AddPyObject()
These functions were undocumented, excluded from the limited C API,
and were only used internally by the compiler.
Add pycore_pyarena.h header. Rename functions:
* PyArena_New() => _PyArena_New()
* PyArena_Free() => _PyArena_Free()
* PyArena_Malloc() => _PyArena_Malloc()
* PyArena_AddPyObject() => _PyArena_AddPyObject()