Add tests based on python's itertools

[natemcintosh]

Feel free to ignore and close this PR without explanation.

The basic idea here is to test the Julia version against the python itertools.

Assumptions: python's itertools library is correct.

• Benefits:
  • Can verify behavior for longer sequences. This could help find corner cases not explored in the current, smaller test set.
  • Greatly expands the test set with only a little code added to the repo.
• Downsides:
  • If the algorithms are ever changed in such a way that the order of combinations/permutations produced changes, these tests will be useless, and will have to be removed.
  • Have to add PyCall as a test dependency. Could make CI take longer to run.

[codecov[bot]]

Codecov Report

Base: 96.97% // Head: 96.97% // No change to project coverage :thumbsup:

Coverage data is based on head (a597eb0) compared to base (8a7a8ac). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #130 +/- ## ======================================= Coverage 96.97% 96.97% ======================================= Files 7 7 Lines 728 728 ======================================= Hits 706 706 Misses 22 22 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaMath). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaMath)

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[natemcintosh]

Looks like the failure on Julia 1.0 on windows is because PyCall failed to build. Not sure how to get around that