Does not use all cores by default

[reportingsjr]

Currently almost all new computers that come out have more than one core and many programs are not taking advantage of this. It would be really easy to add in support to just detect the number of cores a computer have and then set s->threads to that so people wouldn't have to deal with setting this by command line options. A lot of people who use this program may not know any better about this and thus not set the flag.

This line will give you the number of cores a computer has via boost::thread:
unsigned numCores = boost::thread::hardware_concurrency();

I think the old option should be kept, but to add this one a flag such as manualThreads or something would just need to be set true when a person uses the -m/--threads option.

[udoprog]

Fixed in 57aebb5
The default value for number of threads was changed from 1 to your recommendation.
Thanks!