Make the typing information optional.

From Raymond Hettinger:

The make_dataclass() factory function in the dataclasses module currently requires type declarations. It would be nice if the type declarations were optional.

With typing (currently works):

    Point = NamedTuple('Point', [('x', float), ('y', float), ('z', float)])
    Point = make_dataclass('Point', [('x', float), ('y', float), ('z', float)])

Without typing (only the first currently works):

    Point = namedtuple('Point', ['x', 'y', 'z'])          # underlying store is a tuple
    Point = make_dataclass('Point', ['x', 'y', 'z'])      # underlying store is an instance dict