Return a point of the specified dtype.

def astype(self, dtype):
        """Return a point of the specified dtype."""
        if dtype == "int":
            return Point2D( int( round(self.x, 0) ), int( round(self.y, 0) ) )
        elif dtype == "float":
            return Point2D( float(self.x), float(self.y))
        else:
            raise(RuntimeError("Invalid dtype: {}".format(dtype)))