docs/replace.inc: Add |see_cpython|, to xref individual symbols from CPython.

The idea is to use it for each symbol in builtins.rst.

docs/templates/replace.inc

 .. comment: This file is intended for global "replace" definitions.
 
+.. |see_cpython| replace:: See CPython documentation:
+
 .. |see_cpython_module| replace::
 
     *This module implements a subset of the corresponding* `CPython` *module,