Replace Py_INCREF() and Py_XINCREF() with Py_NewRef() and
Py_XNewRef() in test C files of the Doc/ directory.
Replace PyModule_AddObject() with PyModule_AddObjectRef() to simplify
reference counting.
* Add a note to the PyModule_AddObject docs.
* Correct example usages of PyModule_AddObject.
* Whitespace.
* Clean up wording.
* 📜🤖 Added by blurb_it.
* First code review.
* Add < 0 in the tests with PyModule_AddObject
* bpo-33201: Modernize "Extension types" doc
* Split tutorial and other topics
* Some small fixes
* Address some review comments
* Rename noddy* to custom* and shoddy to sublist
* Fix markup
