Reactive code to handle the suspending event and save the state.

save on suspending

    auto ct = std::make_shared<rx::CurrentThreadScheduler>();
    typedef rxrt::EventPattern<Platform::Object^, SuspendingEventArgs^> SuspendingEventPattern;
    rx::from(suspending)
        .chain<rxrt::defer_operation>(
        [](SuspendingEventPattern ep)
        {
            // defer this operation
            return ep.EventArgs()->SuspendingOperation;
        },
        [](rxrt::OperationPattern<SuspendingOperation^>, SuspendingEventPattern)
        {
            // do this while the operation is deferred
            return SuspensionManager::ReactiveSave();
        },
        ct)
        .publish()
        .connect_forever();