code: func (n *NamespacedKV) Int64(key string) (int64, bool) {
  	valBs, err := n.db.Get(n.prefixedKey(key), nil)
  	if err != nil {
  		return 0, false
  	}
  	val := binary.BigEndian.Uint64(valBs)
  	return int64(val), true
  }
docs: // Int64 returns the stored value interpreted as an int64 and a boolean that
  // is false if no value was stored at the key.