[feat] ArraySubsetAssertion

[nikophil]

No description provided.

[kbond]

Really like this implementation!

[kbond]

We should add the not assertions to Expectation: Expectation::notHasSubset() & IsNotSubsetOf().

For allowing json strings, what about leaving ArraySubsetAssertion as-is and having the Expectation method's allow json strings and decode?

[nikophil]

We should add the not assertions to Expectation: Expectation::notHasSubset() & IsNotSubsetOf().

done

For allowing json strings, what about leaving ArraySubsetAssertion as-is and having the Expectation method's allow json strings and decode?

I'd rather do it inside ArraySubsetAssertion because we already have a private method toArray that we apply on both needle and haystack. this would prevent to add a method specific to array subsets inside Expectation class

[kbond]

Looking great! Just one small type check change.

Do you want to merge nikophil#1 into this PR or do it in a separate follow-up?