code: func RangeEnd(key []byte) []byte {
  	end := make([]byte, len(key))
  	copy(end, key)
  	for i := len(end) - 1; i >= 0; i-- {
  		if end[i] < 0xff {
  			end[i] = end[i] + 1
  			end = end[:i+1]
  			return end
  		}
  	}
  	// next key does not exist (e.g., 0xffff);
  	return noEnd
  }
docs: // RangeEnd returns end of the range for given key