Added parallel test cases, refactored parallel benchmarks

[barambani]

This gives the following information on a slowish machine:

Benchmark                                               Mode  Cnt      Score     Error  Units
ParallelLoadLaserdiscCatsBench.parallelLoad1           thrpt  200   5566.682 ±  25.381  ops/s
ParallelLoadLaserdiscCatsBench.parallelLoad2           thrpt  200  13446.380 ±  35.670  ops/s
ParallelLoadLaserdiscCatsRespBench.parallelLoad1       thrpt  200   5823.357 ±  56.710  ops/s
ParallelLoadLaserdiscCatsRespBench.parallelLoad2       thrpt  200  10238.087 ±  55.337  ops/s
ParallelLoadLaserdiscCatsBitVectorBench.parallelLoad1  thrpt  200   7082.593 ±  31.425  ops/s
ParallelLoadLaserdiscCatsBitVectorBench.parallelLoad2  thrpt  200  11236.398 ± 132.632  ops/s
ParallelLoadLaserdiscCatsByteBench.parallelLoad1       thrpt  200  48415.228 ± 189.814  ops/s
ParallelLoadLaserdiscCatsByteBench.parallelLoad2       thrpt  200  52288.273 ± 176.331  ops/s
ParallelLoadLaserdiscCatsBaselineBench.parallelLoad1   thrpt  200  49319.429 ± 387.479  ops/s
ParallelLoadLaserdiscCatsBaselineBench.parallelLoad2   thrpt  200  52857.024 ± 163.238  ops/s
Total time: 28030 s (07:47:10), completed 03-Aug-2020 08:03:43

[sirocchj]

This jump looks indeed suspicious...

ParallelLoadLaserdiscCatsBitVectorBench.parallelLoad2  thrpt  200  11236.398 ± 132.632  ops/s
ParallelLoadLaserdiscCatsByteBench.parallelLoad2       thrpt  200  52288.273 ± 176.331  ops/s

I could not spot anything - good to merge!
Btw... outstanding