Enhancement: Report number of threads in summary report

[Nitsan Wakart]

JMH allows us to set the number of benchmark threads, and to set up thread groups. The number of threads has a potentially large impact on the results but is not reported in the summary. I would like to have the number of threads reported e.g(ignore the values):
Benchmark                   Ts   Mode  Cnt     Score      Error  Units
Contentention.getAndAdd      1   avgt    5    27.300 ±    0.406  ns/op
Contentention.getAndAdd      2   avgt    5   270.300 ±    0.406  ns/op
Contentention.getAndAdd     20   avgt    5  2700.300 ±    0.406  ns/op

The report will be look like this for groups:
Benchmark                     Ts   Mode  Cnt     Score      Error  Units
Contentention.g               22   avgt    5  2270.300 ±    0.406  ns/op
Contentention.g:get            2   avgt    5   270.300 ±    0.406  ns/op

Contentention.g:getAndAdd     20   avgt    5  2700.300 ±    0.406  ns/op