def dict2cols(d, spaces=2, separator=' '):
    """
    Take a dict of string keys and string values, and return a string with
    them formatted as two columns separated by at least ``spaces`` number of
    ``separator`` characters.

    :param d: dict of string keys, string values
    :type d: dict
    :param spaces: number of spaces to separate columns by
    :type spaces: int
    :param separator: character to fill in between columns
    :type separator: str
    """
    if len(d) == 0:
        return ''
    s = ''
    maxlen = max([len(k) for k in d.keys()])
    fmt_str = '{k:' + separator + '<' + str(maxlen + spaces) + '}{v}\n'
    for k in sorted(d.keys()):
        s += fmt_str.format(
            k=k,
            v=d[k],
        )
    return s