Make collection of multiple PMU events available in CLI

[r-belenov]

While Perforator engine supports collecting multiple events, from what I see command-line parsing code always returns array of one element. Also, the code that processes samples marks all of them as cpu:cycle (so I see only cpu:cycle regardless of the actual event). So it looks like current flow is focused on support of cycles only.

Probably collecting many events is out of scope of primary Perforator usage (continous profiling in production) due to higher overhead and no clear benefits. However, even for tuning the software locally Perforator approach looks promising - while the overhead is not so critical, the intrusiveness is, and collecting stacks with current perf or VTune frequently distorts sample distribution over hotspots; hopefully Perforator may work better.

Also, raw values for specific counters are not very useful, possible postprocessing approach is to save collected data in perf format - it should be possible to import it to VTune and use it as a visualization engine.