Add an example showing up how to be in sync on reconnection

[maoueh]

The ultimate goal of the library is to automatically handle the syncing case when reconnecting in the near future.

Right now, this needs to be implemented at the consumer level. A full example showing this would be required so we can quickly point users to it so they can handle it correctly in there own code.

This means:

1. Having an initial undefined start_block on initial connection
2. Having a with_progress flag and record the last seen block
3. On reconnection, re-listen automatically setting start_block to last block seen.

Caveats/To deal with:

1. Most API tokens have access to only -3600 block in the past, we should probably handle that correctly.
2. Explain that in production, last block seen would need to be persisted somehow so that a full crash of the process can recover gracefully to a correct start_block