Add IOverride cache

[bsless]

Speeds up :long benchmark ~2.5x and :mixed ~2x

Closes #87

[brandonbloom]

Thanks for the PR and making the changes! Hopefully I'll have a chance to follow-up / validate next weekend.

[bsless]

Alright, applied all requested changes and fixes (including missed typo)

[bsless]

Gentle bump :)

[brandonbloom]

I haven't forgotten about you. I only really get to work on OSS on weekends, and not every weekend. Thanks for your patience.

[bsless]

Hi @brandonbloom, following up, it's been a while - are there any other changes you'd like me to make in the PR?

[bsless]

Hey, following up again on the PR's first birthday, typo has been fixed long time ago and awaiting your review.
Any other changes you'd like me to make?

[brandonbloom]

These changes seem to break the ClojureScript tests. Please run ./test.sh locally.

Example failure:

ERROR in (pprint-edn) (RangeError:NaN:NaN)
Pretty printing Edn without metadata
expected: (= (clean (with-out-str (pprint data {:width 70}))) wide)
  actual: #object[RangeError RangeError: Maximum call stack size exceeded]

[bsless]

@brandonbloom got around to fixing it, turns out I just needed to increase node's stack size.
Also found out I should have used keyword-identical? thanks to Thomas Heller.

[brandonbloom]

This PR has been included in release v0.6.28! 🎉

[brandonbloom]

This had to be reverted and fixed a different way. See #94