Document new features

[codeliner]

• Add projections via configuration
• How to reuse doctrine connection for PdoEventStore
• How to set up bus-bridge

Example bus bridge from prooph-do-sf

    prooph_event_store_bus_bridge.transaction_manager:
        class: Prooph\EventStoreBusBridge\TransactionManager
        tags:
          - { name: 'prooph_event_store.todo_store.plugin' }

    prooph_event_store_bus_bridge.todo_event_publisher:
        class: Prooph\EventStoreBusBridge\EventPublisher
        arguments: ['@prooph_service_bus.todo_event_bus']
        tags:
          - { name: 'prooph_event_store.todo_store.plugin' }

[webdevilopers]

I'm not sure if my other issues are directly related. But they are related to the EventPublisher:
prooph/service-bus-symfony-bundle#81

Please see the GIST for an example how to bind the publisher to Symfony Messenger Bus. This works fine for me.

I wonder what this integration is supposed to do - maybe something similar?
https://github.com/prooph/event-store-symfony-bundle/blob/master/doc/messenger.md