Helping function of `_parse_feature_names` that parses a dictionary of feature names.

def _parse_names_dict(feature_names):
        """Helping function of `_parse_feature_names` that parses a dictionary of feature names."""
        feature_collection = OrderedDict()
        for feature_name, new_feature_name in feature_names.items():
            if isinstance(feature_name, str) and (isinstance(new_feature_name, str) or
                                                  new_feature_name is ...):
                feature_collection[feature_name] = new_feature_name
            else:
                if not isinstance(feature_name, str):
                    raise ValueError('Failed to parse {}, expected string'.format(feature_name))
                else:
                    raise ValueError('Failed to parse {}, expected string or Ellipsis'.format(new_feature_name))
        return feature_collection