code: func ConstructPartialCompositeHistoryKey(ns string, key string, endkey bool) []byte {
  	var compositeKey []byte
  	compositeKey = append(compositeKey, []byte(ns)...)
  	compositeKey = append(compositeKey, CompositeKeySep...)
  	compositeKey = append(compositeKey, []byte(key)...)
  	compositeKey = append(compositeKey, CompositeKeySep...)
  	if endkey {
  		compositeKey = append(compositeKey, []byte{0xff}...)
  	}
  	return compositeKey
  }
docs: //ConstructPartialCompositeHistoryKey builds a partial History Key namespace~key~
  // for use in history key range queries