Add `parallel` option to `multi_irace`.

[Saethox]

Closes #59.

I personally don't need more than this, so I'm happy with this level of functionality.

[MLopez-Ibanez]

I personally don't need more than this, so I'm happy with this level of functionality.

Fair enough. Could you add an error for windows?

The failed check in Windows is something that I will fix soon (hopefully).

[MLopez-Ibanez]

Hi, I did a force-push in master.

Could you rebase on the tip of master and squash commits? I will merge it once it is done. Thanks!

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@f5f690a). Click here to learn what that means. The diff coverage is 76.47%.

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