The Prooph\EventStore\Snapshot\* classes are now moved to their own repository, SnapshotStore.
The Prooph\EventStore\Aggregate\* classes are now moved into the event-sourcing repository.
The event store now ships with a Prooph\EventStore\ReadOnlyEventStore and a Prooph\EventStore\EventStore interface.
No event store adapters exist anymore, instead there are different implementations of the event store.
In order to use action events like in v6, you need to wrap your event store.
$eventStore = new ActionEventEmitterEventStore($eventStore);
or
$eventStore = new TransactionalActionEventEmitterEventStore($eventStore);
Also, there are no more .pre and .post commit hooks anymore, instead, this is handled with different priorities now.
Instead of calling
$plugin->setUp($eventStore);
you now need to call
$plugin->attachToEventStore($eventStore);
If you are using the event-store together with the event-sourcing component, most stuff is pretty much unchanged for you, as you don't interact with the event store directly (this is done by the event-sourcing component).
If you are making calls to the event store yourself, take a look at the event_store docs on how the new usage is.
If you are using v6 with MySQL (using doctrine adpater) and you want to switch to v7 with MySQL (using pdo-event-store), you need to upgrade your database before you do this (same for other db vendors of course). The way events are persisted has changed and you cannot simply update your source code to make this change. You need to write a migration script, take the database offline, perform the migration and go back online.
Things to do to migrate:
This would need to be done for all event streams.
As this is a very tough job, we don't provide any migration script currently. For some applications, a downtime is not acceptable, in which case v7 might not be the right choice. You should use it when you can take the application offline for a while and perform the DB migration, or you can wait until you start a new project to use it.
We will support v6 series with bugfixes until 3 Dec 2017.