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.
All public field comments should start with the field's name. (The other fields are poorly documented, sorry.)

The doc should say "DisableCompression disables decompress response if set" or something similar. Applies to DisableKeepAlives too.