code: func (db *DB) RangeLimitIterator(min []byte, max []byte, rangeType uint8, offset int, count int) *RangeLimitIterator {
  	return NewRangeLimitIterator(db.NewIterator(), &Range{min, max, rangeType}, &Limit{offset, count})
  }
docs: //count < 0, unlimit.
  //
  //offset must >= 0, if < 0, will get nothing.