- This PR fixes situation to avoid underflow, this is possible
because of disconnected operations in replay/sendEvents
- Hold right locks if Del() operation is performed in Get()
- Remove panic in the code and use loggerOnce
- Remove Timer and instead use Ticker instead for proper ticks
This patch includes the following changes in event store interface
- Removes memory store. We will not persist events in memory anymore, if `queueDir` is not set.
- Orders the events before replaying to the broker.
- The events will be persisted in queueStore if `queueDir` is set.
- Else, if queueDir is not set events persist in memory.
The events are replayed back when the mqtt broker is back online.
