Summary

Kotlin and Java reactors and reducers reach parity with the C# client on observation behavior.

Added

@Reactor and @Reducer take an eventSequence, for observing a sequence other than the event log.
@Reducer takes isActive, for a reducer the kernel does not actively run.
@OnceOnly excludes a reactor from replay on the class, or a single handler on a method.
@Replay marks the handler that takes over while an observer is being replayed.
Reducer handlers can take an EventContext after the state.
EventContext carries the observation state, event source type, event stream type and id, event store, namespace, causation, tags, and hash.

Handler shapes the client cannot invoke now fail at register() instead of on every event. (#17)

EventContext.correlationId was a random value and causedBy was always Identity.unknown; both are now read from the kernel.