code: public <IN, OUT> Processor<IN, OUT> newAsyncProcessor(Function<IN, OUT> processingFunction) {
          return newAsyncProcessor(processingFunction, scheduler, batchSize);
      }
docs: create async processor. Usually not called directly (see EventSink+RxPublisher)
  
  @param processingFunction
  @param <IN>
  @param <OUT>
  @return