Low-Level-Design/distributed-event-bus

1) Multiple publishers and subscribers (Register from any class to eventbus)
2) Causal ordering of topics
3) Supports configurable retry attempts.
4) Have a dead letter queue.
5) Idempotency on event receiving
6) Allow both pull and push models
7) Allow subscribing from a timestamp or offset
8) Allow preconditions for event subscription

Optional features:
1) Add database support, with flushing on threshold.
2) Retrieve K elements together for subscriber.