Added Left-Right guard to compare with WriterReaderPhaser

Hi,
I've added a Left-Right pattern with a Ingress/Egress ReadIndicator using LongAdder counters to reduce contention (and false-sharing) as needed on the arrive() method.
http://concurrencyfreaks.com/2014/11/a-catalog-of-read-indicators.html

I did some performance measurements against WriterReaderPhaser but for this scenario the gains were very small, because it seems that the bottleneck is on the counters of the histogram itself, and therefore, improving the arrive() does little benefit.

Feel free to disregard this pull request, it's just to show that any variant of the Left-Right is a replacement for WriterReaderPhaser, because the WriterReaderPhaser is also a variant of Left-Right  ;)