Specific integers

[JamieBallingall]

Add two constant values: minInt and maxInt. Similar in spirit to PR #48 but provides the bounds on 32-bit signed integers (i.e., the Int type) as Int rather than referencing Javascript's concept of minimum and maximum integers.

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Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)

[JamieBallingall]

I just realized that Int has a perfectly good Bounded instance, so minInt and maxInt are redundant.