Depeche-db

* Allow `ack` in client transaction: This allows for `exactly once` delivery semantics
* **BREAKING CHANGE**: Change DB object names
* AggregatedStream: `{name}_projected_stream` -> `depeche_stream_{name}`
* see `AggregatedStream.[get_migration_ddl|migrate_db_objects]`
* MessageStore (ie. Storage): `{name}_messages` -> `depeche_msgs_{name}`
* see `Storage.[get_migration_ddl|migrate_db_objects]`
* DbSuscriptionStateProvider: `{name}_subscription_state` -> `depeche_subscriptions_{name}`
* see `DbSuscriptionStateProvider.[get_migration_ddl|migrate_db_objects]`

* Add `global_position_to_positions` method on aggregated stream

**Full Changelog**: https://github.com/depeche-py/depeche-db/compare/v0.6.2...v0.7.0

* Add `register_manual` method to `MessageHandlerRegister`

* Add small event sourcing lib

* Nicer interface to create `AggregatedStream` & `Subscription`
* Move runner back onto `Subscription`
* Improved exceptions