Add an option to store profiling information

[tebeka]

In some cases I'd like to investigate the profiling information after the benchmark, maybe with snakeviz.

I suggest adding --benchmark-cprofile-save=FILE that will save the cProfile information (pstats) to FILE.

If this flag is specific, it implies that ---benchmark-cprofile is set as well. Maybe with cumtime if not explictly specified.