add cpu usage report, add multi core support. Add optional undefined …

[Qubasa]

Hey there, this PR is a bit more controversial as it add automatic forking and opens up multiple consecutive ports, and also reports the CPU usage, if you don't wanna merge it like this I understand :-)

[rbruenig]

Hi, thank you for another PR :) I'll have a proper look on the weekend. Changes seem resonable to on first glance. Only question is regarding the num_cores cmd argument. Do I understand it correctly, that this will spawn n instances that each use/listen on their own port? If that's the case, we might want to rename the option, because it might be misleading for users. It's seems more like a "spawn x instances" option, instead of making a single instance multithreaded

[Qubasa]

@rbruenig Yes that's exactly what it does. Hmm yeah a renaming is a good idea, I changed it now to -i num number of instances to start

[rbruenig]

@Qubasa Thanks, I think that makes it much clearer.

Code otherwise looks good to me, except that the cpu-usage.c doesn't quite match the code formatting of the rest of the repository. If we apply the following cosmetic changes, I will merge the code:

• file names should use _ instead of - in between words
• All if / else statements should use parenthesese ({ }), even if the following statement is only a single line
• Indent size should be 4 spaces

Could you apply these changes :) ?