Add the :c:func:`Py_Is(x, y) <Py_Is>` function to test if the *x* object is the
*y* object, the same as ``x is y`` in Python. Add also the :c:func:`Py_IsNone`,
:c:func:`Py_IsTrue`, :c:func:`Py_IsFalse` functions to test if an object is,
respectively, the ``None`` singleton, the ``True`` singleton or the ``False``
singleton.
Patch by Victor Stinner.
