++++++++++++++++++
Deprecate old APIs
++++++++++++++++++

CPython is old, the code evolved. Some functions became useless and so should
be removed. But backward compatibility matters in Python, so we need a
transition period with a deprecation process.

The deprecation can be:

* Emitted at runtime: ``DeprecationWarning``
* At the compilation: ``Py_DEPRECATED()``
* In the documentation

Functions that should deprecated:

* Unicode functions using ``Py_UNICODE`` type
* ``Py_VA_COPY()``: use directly standard ``va_copy()``,
  see `email <https://mail.python.org/pipermail/python-dev/2016-September/146537.html>`_
* ``Py_MEMCPY()``: `kept for backwards compatibility
  <http://github.com/python/cpython/commit/f051e43b22af014364e231c36489e6745993ea34>`_

See:

* https://bugs.python.org/issue19569
*