Add constants epsilon, minPosNumber and maxNumber

[JamieBallingall]

Add constants: epsilon, minPosNumber and maxNumber as explicit values without any foreign imports. The values are the same value as the Javascript Number object properties EPSILON, MIN_VALUE and MAX_VALUE.

Closes issue #23 and replaces PR #19. Differences to PR #19:

• Values are explicit rather than imported from the Javascript Number object
• The value NEGATIVE_INFINITY is not implemented, since -infinity works just fine

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)