Package topics deals with MQTT topic names, topic filters and subscriptions. - "Topic name" is a / separated string that could contain #, * and $ - / in topic name separates the string into "topic levels" - # is a multi-level wildcard, and it must be the last character in the
topic name. It represents the parent and all children levels.
- + is a single level wildwcard. It must be the only character in the
topic level. It represents all names in the current level.
- $ is a special character that says the topic is a system level topic