Cookbook ideas for num_cpus

[bobbo]

Come up with ideas for nice introductory examples of using the num_cpus crate, possibly in combination with other crates, that would be good to show in the Rust Cookbook. Please leave a comment here with your ideas! You don't necessarily have to write the example code yourself but PRs are always welcome!

EDIT:

• Draw a fractal using a threadpool - uses num_cpus - and basically all the other threadpool examples that are going to be implemented
• Check number of logical cpu cores

[budziq]

@bobbo I've added a single example idea for now.
Another is to "Get number of physical cpu cores" unfortunately I do not like that the get_physical falls back to logical cores if physical cant be queried making such example unreliable (I'would suggest for this function to return a Result) I'll propose it on blitz evaluation thread.

[AndyGauge]

This tracking issue seems resolved.