Add validation for exclusiveMinimum

[veepeeaee]

PR to add functionality requested in #20

In addition to existing checks, makes adding exclusiveMinimum: true to a minimum clause a breaking change

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[everettraven]

While setting exclusiveMinimum and minimum are pretty tightly coupled, I think this would make more sense to be an entirely separate check than integrated as part of the minimum check.

I've historically tried to separate each of these validations to check a singular schema property to keep scope as small as possible until we explicitly need to start coupling checks together to unlock more advanced use cases. Keeping to that pattern for now would be my preference.