The HdrHistogramReader makes some problematic assumptions on the roles
played by start time, base time and histogram start/end times. This is
to be revisited in a future release of HdrHistogram (see
https://github.com/HdrHistogram/HdrHistogram/issues/69). In the meantime
this change will make YCSB record as expected by the reader:
a. Set histogram log base time (same as start time)
b. Only create the recorder after the log has been setup

final, refactor repeated export code from subclasses.

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.