Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Includes/cpython/method.pxd

+cdef extern from "Python.h":
+    ctypedef void PyObject
+    ############################################################################
+    # 7.5.4 Method Objects
+    ############################################################################
+
+    # There are some useful functions that are useful for working with method objects.
+    # PyTypeObject PyMethod_Type
+    # This instance of PyTypeObject represents the Python method type. This is exposed to Python programs as types.MethodType.
+
+    bint PyMethod_Check(object o)
+    # Return true if o is a method object (has type
+    # PyMethod_Type). The parameter must not be NULL.
+
+    object PyMethod_New(object func, object self, object cls)
+    # Return value: New reference.
+    # Return a new method object, with func being any callable object;
+    # this is the function that will be called when the method is
+    # called. If this method should be bound to an instance, self
+    # should be the instance and class should be the class of self,
+    # otherwise self should be NULL and class should be the class
+    # which provides the unbound method..
+
+    PyObject* PyMethod_Class(object meth) except NULL
+    # Return value: Borrowed reference.
+    # Return the class object from which the method meth was created;
+    # if this was created from an instance, it will be the class of
+    # the instance.
+
+    PyObject* PyMethod_GET_CLASS(object meth)
+    # Return value: Borrowed reference.
+    # Macro version of PyMethod_Class() which avoids error checking.
+
+    PyObject* PyMethod_Function(object meth) except NULL
+    # Return value: Borrowed reference.
+    # Return the function object associated with the method meth.
+
+    PyObject* PyMethod_GET_FUNCTION(object meth)
+    # Return value: Borrowed reference.
+    # Macro version of PyMethod_Function() which avoids error checking.
+
+    PyObject* PyMethod_Self(object meth) except? NULL
+    # Return value: Borrowed reference.
+    # Return the instance associated with the method meth if it is bound, otherwise return NULL.
+
+    PyObject* PyMethod_GET_SELF(object meth)
+    # Return value: Borrowed reference.
+    # Macro version of PyMethod_Self() which avoids error checking.