Why Parallel.processor_count do not use standard Etc.nprocessors?

[zekefast]

There is a standard method in Ruby 2.2.0: Etc.nprocessors

I think it would be better to rely on method from standard library instead of implemented it in system dependent way like done in [the code](https://github.com/grosser/parallel/blob/master/lib/parallel/processor_count.rb#L17]

What do you think?

Disclaimer: I have not tested all supported by Parallel.processor_count platforms to ensure that Etc.nprocessors behaves on them correctly.

[christiankakesa]

Etc.nprocessors might return a smaller number of cpus than physical number of cpus. The way Parallel.processor_count proceeds is a better approach ; no weird things are done. But we probably need both.

[grosser]

The result might be smaller number than physical cpus especially when ruby process is bound to specific cpus. This is intended for getting better parallel processing.

that sounds fine to me / like a feature ... can you make a PR to use it when it's available (RUBY_VERSION > '2.2.0') ?

[zekefast]

@FeNicks Thanks.
@grosser yes, I will try to submit it this weekend. Thanks!