Add some important features

Hi!

Please, accept this pull request for adding this features:

- disable-compression - for speed up benchmark (no need spend cpu time to decompress)
- disable-keepalive      - for test scenario where client don't support keep-alive
- cpus                          - useful option flag for avoid using GOMAXPROCS.

Thanks,
Artem Andreenko.
By default, you shouldn't be utilising all CPUs you have. For low number of n and c, it will make boom slower.

The default should be -1, and runtime.GOMAXPROCS(*flagCpus) should be called if this flag's value is bigger than -1.