Adding cython v0.20.2 in third-party.

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

Index: third_party/cython/src/Cython/Includes/cpython/mapping.pxd
diff --git a/third_party/cython/src/Cython/Includes/cpython/mapping.pxd b/third_party/cython/src/Cython/Includes/cpython/mapping.pxd
new file mode 100644
index 0000000000000000000000000000000000000000..3d235b65e20c0a774004bb0fd0938b158d515bb1
--- /dev/null
+++ b/third_party/cython/src/Cython/Includes/cpython/mapping.pxd
@@ -0,0 +1,64 @@
+cdef extern from "Python.h":
+
+    ############################################################################
+    # 6.4 Mapping Protocol
+    ############################################################################
+
+    bint PyMapping_Check(object o)
+    # Return 1 if the object provides mapping protocol, and 0
+    # otherwise. This function always succeeds.
+
+    Py_ssize_t PyMapping_Length(object o) except -1
+    # Returns the number of keys in object o on success, and -1 on
+    # failure. For objects that do not provide mapping protocol, this
+    # is equivalent to the Python expression "len(o)".
+
+    int PyMapping_DelItemString(object o, char *key) except -1
+    # Remove the mapping for object key from the object o. Return -1
+    # on failure. This is equivalent to the Python statement "del
+    # o[key]".
+
+    int PyMapping_DelItem(object o, object key) except -1
+    # Remove the mapping for object key from the object o. Return -1
+    # on failure. This is equivalent to the Python statement "del
+    # o[key]".
+
+    bint PyMapping_HasKeyString(object o, char *key)
+    # On success, return 1 if the mapping object has the key key and 0
+    # otherwise. This is equivalent to the Python expression
+    # "o.has_key(key)". This function always succeeds.
+
+    bint PyMapping_HasKey(object o, object key)
+    # Return 1 if the mapping object has the key key and 0
+    # otherwise. This is equivalent to the Python expression
+    # "o.has_key(key)". This function always succeeds.
+
+    object PyMapping_Keys(object o)
+    # Return value: New reference.
+    # On success, return a list of the keys in object o. On failure,
+    # return NULL. This is equivalent to the Python expression
+    # "o.keys()".
+
+    object PyMapping_Values(object o)
+    # Return value: New reference.
+    # On success, return a list of the values in object o. On failure,
+    # return NULL. This is equivalent to the Python expression
+    # "o.values()".
+
+    object PyMapping_Items(object o)
+    # Return value: New reference.
+    # On success, return a list of the items in object o, where each
+    # item is a tuple containing a key-value pair. On failure, return
+    # NULL. This is equivalent to the Python expression "o.items()".
+
+    object PyMapping_GetItemString(object o, char *key)
+    # Return value: New reference.
+    # Return element of o corresponding to the object key or NULL on
+    # failure. This is the equivalent of the Python expression
+    # "o[key]".
+
+    int PyMapping_SetItemString(object o, char *key, object v) except -1
+    # Map the object key to the value v in object o. Returns -1 on
+    # failure. This is the equivalent of the Python statement "o[key]
+    # = v".
+