Add more performance counters

[ilyapopov]

Currently nanobench uses a few hardware performance counters - number of instructions retired, cycles, etc..

I would like to have data on cache performance. Specifically, there are counters for cache references and cache misses.

In Linux, there are portable counters PERF_COUNT_HW_CACHE_REFERENCES and PERF_COUNT_HW_CACHE_MISSES,
and also there are more specialized events PERF_COUNT_HW_CACHE_L1D etc.

Is there a reason to not use these? If not, I may be able to work on this.