feat: add “regression” suite of sorts (#60)

* feat: provide a custom `isSorted` function for determining whether a slice is sorted ascending.

Inject the function into the playground, and fix the test that needs to verify sort order.

fixes #5

* remove superfluous sort

* feat: add “regression” suite of sorts

Something to run against the examples in the Playground to ensure we don’t accidentally publish an example that should work and doesn’t.

* Add license header