code: func (store *MemoryStore) Del(key string) {
  	store.Lock()
  	defer store.Unlock()
  	if !store.opened {
  		ERROR.Println(STR, "Trying to use memory store, but not open")
  		return
  	}
  	mid := mIDFromKey(key)
  	m := store.messages[key]
  	if m == nil {
  		WARN.Println(STR, "memorystore del: message", mid, "not found")
  	} else {
  		delete(store.messages, key)
  		DEBUG.Println(STR, "memorystore del: message", mid, "was deleted")
  	}
  }
docs: // Del takes a key, searches the MemoryStore and if the key is found
  // deletes the Message pointer associated with it.