Fix EventStore.getConsumer returning Consumer instance

[albe]

This change removes the EventUnwrapper transform stream from EventStore.getConsumer(), which made the method return a stream.Transform instead of an instance of Consumer.
This means that the Consumer from an EventStore receives stored event structures, which constist of { stream: string, payload: object, metadata: object }, where payload corresponds to the original event that was committed.

Resolves #172

[coveralls]

Coverage decreased (-0.008%) to 97.718% when pulling 38a5694 on consumer-fixes into 8a6d93a on main.