code: public Closeable onRawOrderbookEvent(final BiConsumer<BitfinexOrderBookSymbol, Collection<BitfinexOrderBookEntry>> listener) {
          rawOrderbookEntryConsumers.offer(listener);
          return () -> rawOrderbookEntryConsumers.remove(listener);
      }
docs: registers listener for raw orderbook events
  @param listener of event
  @return hook of this listener