Function flatten_buffer_result 

pub fn flatten_buffer_result<T: Clone + 'static, K: Clone + 'static, C: IChangeSet<T, K>>(
    source: Rc<dyn IObservable<Vec<C>>>,
) -> Rc<dyn IObservable<ChangeSet<T, K>>>

The buffers of change sets, each as one change set; the empty buffers are left out (FlattenBufferResult(IObservable<IList<IChangeSet<TObject, TKey>>>)).