Convert a single region or multiple region specification into multiregion list.

    If a single region (chrom, start, end), returns [(chrom, start, end)]
    otherwise returns multiregion.

def to_multiregion(region):
    """Convert a single region or multiple region specification into multiregion list.

    If a single region (chrom, start, end), returns [(chrom, start, end)]
    otherwise returns multiregion.
    """
    assert isinstance(region, (list, tuple)), region
    if isinstance(region[0], (list, tuple)):
        return region
    else:
        assert len(region) == 3
        return [tuple(region)]