code: func newMemoryNodeDB(self NodeID) (*nodeDB, error) {
  	db, err := leveldb.Open(storage.NewMemStorage(), nil)
  	if err != nil {
  		return nil, err
  	}
  	return &nodeDB{
  		lvl:  db,
  		self: self,
  		quit: make(chan struct{}),
  	}, nil
  }
docs: // newMemoryNodeDB creates a new in-memory node database without a persistent
  // backend.