code: func (n *NamespacedKV) PutInt64(key string, val int64) {
  	var valBs [8]byte
  	binary.BigEndian.PutUint64(valBs[:], uint64(val))
  	n.db.Put(n.prefixedKey(key), valBs[:], nil)
  }
docs: // PutInt64 stores a new int64. Any existing value (even if of another type)
  // is overwritten.