3.1')
    ((3, 1), None)
    >>> parse_pycentral_vrange('<< 4.0')
    (None, (4, 0))
    >>> parse_pycentral_vrange('3.1')
    ((3, 1), (3, 1))
    >>> parse_pycentral_vrange('3.1, 3.2')
    ((3, 1), None)
    Nr