code: func ForeachInRange(kv KeyValue, start, end string, fn func(key, value string) error) error {
  	it := kv.Find(start, end)
  	for it.Next() {
  		if err := fn(it.Key(), it.Value()); err != nil {
  			it.Close()
  			return err
  		}
  	}
  	return it.Close()
  }
docs: // ForeachInRange runs fn for each key/value pair in kv in the range
  // of start and end, which behave the same as kv.Find. If fn returns
  // an error, that same error is returned from Foreach and iteration
  // stops.