repr for vso.attrs.Wave

# Issue URL: https://github.com/sunpy/sunpy/issues/532

class Wave(Attr, _Range):
    def __init__(self, wavemin, wavemax, waveunit='Angstrom'):
        self.min, self.max = sorted(
            to_angstrom(v, waveunit) for v in [float(wavemin), float(wavemax)]
        )
        self.unit = 'Angstrom'

        Attr.__init__(self)
        _Range.__init__(self, self.min, self.max, self.__class__)

    def collides(self, other):
        return isinstance(other, self.__class__)

    def __repr__(self):
    return 'Min: {0}, Max: {1}, Units Used: {2}'.format(self.min, self.max, self.unit)