closes #239.

Origin patch in PR-286.

client (worker) thread completing via a CountDownLatch.

Fixes #316

(trailing whitespaces, 2 spaces instead of tabs and e.t.c)

* returncodes -> OneMeasurement
* HashMap -> ConcurrentHashMap

Closes gh-353

- Make status interval configurable

- Output old histogram or HdrHistogram or both
- Potentially output HdrHistogram to log file on status interval.

Add a joined histogram measuremement to compare old/new histogram
outputs.

Add option for controlling the feature(default on).

Remove needless synchronization by using CHM in Measurements.

Add option to randomize delay(default=true, as before)

throttle method in client.

 [exporter] added JSONArrayMeasurementsExporter which generates one JSON array of measurement objects.

Given the min and max parameter ZipfianGenerator  should not return 0 if (uz < 1) nor 1 if (uz<1.0+Math.pow(0.5,theta)). Instead it should return the min value (base) or min + 1.

closes #237.

* Time the cleanUp of a DBWrapper
* For HBase this clean up should also be counted as an update.

specified keys. When running a workload, read data is checked against the
deterministic value and inconsistencies exported to the measurements object.

Discovered flaws in multithreaded YCSB 'latest' workload distribution as
data may be read by one thread before it is written by another.

Fixed bug in CoreWorkload. Read-Modify-Write latency should be reported in microseconds, not milliseconds.