Do the work of picking an alignment split size for the given criteria.

def _pick_align_split_size(total_size, target_size, target_size_reads, max_splits):
    """Do the work of picking an alignment split size for the given criteria.
    """
    # Too many pieces, increase our target size to get max_splits pieces
    if total_size // target_size > max_splits:
        piece_size = total_size // max_splits
        return int(piece_size * target_size_reads / target_size)
    else:
        return int(target_size_reads)