Universal

• Renames Mutation to Event.
• Removes deprecated APIs.
• Adds the most general version of feedback loop

public func react<State, Request: Equatable, RequestID, Event>(
    requests: @escaping (State) -> [RequestID: Request],
    effects: @escaping (_ initial: Request, _ state: Observable<Request>) -> Observable<Event>
) -> (ObservableSchedulerContext<State>) -> Observable<Event> {

• Simpler feedback loops are now just a specialization of the general one.
• Removes hacky versions of feedback loops that existed because Swift compiler didn't generate automatic Equality conformance.