Support Yields section in traitsdoc too.

Author: chebee7i

numpydoc/traitsdoc.py

@@ -61,6 +61,7 @@ def __init__(self, cls, modulename='', func_doc=SphinxFunctionDoc):
             'Extended Summary': [],
             'Parameters': [],
             'Returns': [],
+            'Yields': [],
             'Raises': [],
             'Warns': [],
             'Other Parameters': [],