Processor multiprocessing

[mjtadema]

This is what i came up with for multiprocessing in the base run_system method. It will always fall back to the old method if nproc is not set. So far it seems to work fine in combination with my changed make_bonds function in #234 .

[mjtadema]

It seems we need to add a test for run_system with multiprocessing, but I am not entirely sure where to put it..

[mjtadema]

Some small comments. The downside of this approach is that every Processor being run creates it's own Pool of processes, which might create a lot of overhead. I'm not sure how bad it is though.

Instead of setting the class attribute nproc and creating the pool in run_system, maybe we can set the attribute to be the actual pool itself. That way the same pool should be shared among all processors, no?

[pckroon]

Yes, that would be an option.

[fgrunewald]

stale PR; also it's so far behind it will probably be easier to make a new one.