Adding input param of num_cores to ThreadPool::new()

[robinbernon]

In keeping to a similar input style to the rust-threadpool crate: https://github.com/rust-threadpool/rust-threadpool/blob/master/src/lib.rs#L367 thought it would be best to have the new input param as num_cores.

[alecmocatta]

Thanks @robinbernon, looks good! Two things: would you be able to make the same change to ProcessPool::new, and given its ordering (fn new(processes: Option<usize>, tasks_per_core: Option<usize>, resources: Resources)), perhaps num_cores could come before tasks_per_core for both methods, and also be renamed just cores?

[robinbernon]

Thanks @robinbernon, looks good! Two things: would you be able to make the same change to ProcessPool::new, and given its ordering (fn new(processes: Option<usize>, tasks_per_core: Option<usize>, resources: Resources)), perhaps num_cores could come before tasks_per_core for both methods, and also be renamed just cores?

Have added cores input for ProcessPool and also changed the input param from num_cores => cores.