[性能相关]PEP draft： Hide implementation details in the C API

虽然只是开始阶段，但是起码描绘的场景还是不错的。不过就看保守的 py 社区怎么看了。

Modify the C API to remove implementation details. Add an opt-in option
to compile C extensions to get the old full API with implementation
details.

The modified C API allows to more easily experiment new optimizations:

* Indirect Reference Counting
* Remove Reference Counting, New Garbage Collector
* Remove the GIL
* Tagged pointers

Reference counting may be emulated in a future implementation for
backward compatibility.

https://mail.python.org/pipermail/python-ideas/2017-July/046399.html