Add Zachary's Karate Club

[IvanIsCoding]

Adds the famous Zachary's karate club, a network that is used in many examples.

Makes #1277 easier and I assume it will be used in lots of example for community detection algorithms

[coveralls]

Pull Request Test Coverage Report for Build 11859929189

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 109 of 109 (100.0%) changed or added relevant lines in 2 files are covered.
• 67 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.009%) to 95.834%

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Files with Coverage Reduction	New Missed Lines	%
src/iterators.rs	67	74.78%

Totals
Change from base Build 11709175986:	0.009%
Covered Lines:	18125
Relevant Lines:	18913

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💛 - Coveralls

[mtreinish]

Overall this LGTM thanks for adding this generator. I just have a few inline comments that will slightly improve the performance and/or simplify the code.

[mtreinish]

LGTM, thanks for making the updates.