Add tests for quot, rem, and mod

[dgr]

Add tests for:

• quot
• rem
• mod

Also adds a file called portability.cljc in which we can add various portability functions.

[jeaye]

We probably want a reader conditional here, right? If CLJ, use instance?, otherwise, use the generic check?

[dgr]

We could, but that makes it very specific to JVM. The doc strings say that int? returns true for a fixed-width integer, whereas integer? returns true for all integers, whether fixed with or big. So, I figured this would be slightly more portable than a direct class check using instance?.

[jeaye]

Yep, I hear you. I was just wondering about the odds that there's an integer among Clojure dialects which isn't int? and which isn't a big int. 🤔 Maybe not worth considering.

[dgr]

I thought about that and decided we could cross that bridge later. It's easy enough to rewrite at that time.

[jeaye]

Nice work! 💪