Support old limited C API

Add a PyIter_NextItem() implementation for limited C API 3.3 and
older.

Add a INIT_FUNC() implementation for limited C API 3.4 and older.

Author: vstinner

docs/api.rst

@@ -809,7 +809,9 @@ PyThreadState
 
    See `PyThreadState_GetID() documentation <https://docs.python.org/dev/c-api/init.html#c.PyThreadState_GetID>`__.
 
-   Availability: Python 3.7. Not available on PyPy.
+   Availability: Python 3.7.
+
+   Not available on PyPy nor on limited C API 3.8 and older.
 
 PyInterpreterState
 ^^^^^^^^^^^^^^^^^^
@@ -933,7 +935,9 @@ part of the Python C API.
 
 .. c:function:: PyFrameObject* _PyThreadState_GetFrameBorrow(PyThreadState *tstate)
 
-   :c:func:`PyThreadState_GetFrame` variant. Not available on PyPy.
+   :c:func:`PyThreadState_GetFrame` variant.
+
+   Not available on PyPy nor with the limited C API 3.8 and older.
 
    Not available on limited C API 3.8 and older.
 

docs/changelog.rst

@@ -1,7 +1,8 @@
 Changelog
 =========
 
-* 2026-10-06: Add functions:
+* 2026-10-08: Add support for the limited C API 3.2.
+* 2026-10-08: Add functions:
 
   * ``PyImport_ImportModuleAttr()``
   * ``PyImport_ImportModuleAttrString()``