Flip normals of a triangular mesh by reversing the point ordering.

def flip_normals(self):
        """
        Flip normals of a triangular mesh by reversing the point ordering.

        """
        if self.faces.size % 4:
            raise Exception('Can only flip normals on an all triangular mesh')

        f = self.faces.reshape((-1, 4))
        f[:, 1:] = f[:, 1:][:, ::-1]