Add missing "@cython.binding" decorator for Python code.

CHANGES.rst

@@ -62,6 +62,8 @@ Features added
 * ``--no-docstrings`` option added to ``cythonize`` script.
   Original patch by mo-han.  (Github issue #2889)
 
+* The ``@cython.binding`` decorator is available in Python code.
+
 Bugs fixed
 ----------
 

Cython/Shadow.py

@@ -123,6 +123,8 @@ overflowcheck.fold = optimization.use_switch = \
 
 final = internal = type_version_tag = no_gc_clear = no_gc = _empty_decorator
 
+binding = lambda _: _empty_decorator
+
 
 _cython_inline = None
 def inline(f, *args, **kwds):