Format episode number(s) into string, using configured values.

def _format_episode_numbers(episodenumbers):
    """Format episode number(s) into string, using configured values."""
    if len(episodenumbers) == 1:
        epno = cfg.CONF.episode_single % episodenumbers[0]
    else:
        epno = cfg.CONF.episode_separator.join(
            cfg.CONF.episode_single % x for x in episodenumbers)

    return epno