Set::union() method added

[Smoren]

Hi @markrogoyski,

I've added new methods and covered them by tests:

• Set::union()
• Set::unionCoercive()
• Stream::unionWith()
• Stream::unionCoerciveWith()

[coveralls]

Pull Request Test Coverage Report for Build 4368218265

• 6 of 6 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 99.868%

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Totals
Change from base Build 4361445493:	0.001%
Covered Lines:	758
Relevant Lines:	759

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💛 - Coveralls

[Smoren]

This branch is rebased from develop.

[markrogoyski]

Hi @Smoren,

Thanks for the PR. It's neat that you were able to make use of partialIntersection to implement it.

Mark

[Smoren]

Thank you for merging this PR!