Turn a string of extras into a parsed extras list

def parse_extras(extras_str):
    # type: (AnyStr) -> List[AnyStr]
    """
    Turn a string of extras into a parsed extras list
    """

    from pkg_resources import Requirement

    extras = Requirement.parse("fakepkg{0}".format(extras_to_string(extras_str))).extras
    return sorted(dedup([extra.lower() for extra in extras]))