Returns a merged metadata info dictionary from the supplied
        function and additional dictionaries

def _merge_metadata(self_or_cls, obj, fn, *dicts):
        """
        Returns a merged metadata info dictionary from the supplied
        function and additional dictionaries
        """
        merged = dict([(k,v) for d in dicts for (k,v) in d.items()])
        return dict(merged, **fn(obj)) if fn else merged