Add assertions for `NonEmptyList<A>` type

[rcardin]

Add assertions for NonEmptyList<A> type. As an example, take a look at the assertions list implemented by Kotest library for such type.

NonEmptyList
nel.shouldContain(e)	Asserts that the NonEmptyList contains the given element e
nel.shouldContainAll(e1,e2,...,en)	Asserts that the NonEmptyList contains all the given elements e1,e2,...,en
nel.shouldContainNull()	Asserts that the NonEmptyList contains at least one null
nel.shouldContainNoNulls()	Asserts that the NonEmptyList contains no nulls
nel.shouldContainOnlyNulls()	Asserts that the NonEmptyList contains only nulls or is empty
nel.shouldHaveDuplicates()	Asserts that the NonEmptyList has at least one duplicate
nel.shouldBeSingleElement(e)	Asserts that the NonEmptyList has a single element which is e
nel.shouldBeSorted()	Asserts that the NonEmptyList is sorted

[farajist]

This seems interesting @rcardin, I will give it a shot if you haven't already started on it, it's been a while 😄 !

[rcardin]

Hey, man. Yep, if you want, it’s yours. Let me know.

Cheers

[farajist]

Let's gooo 🚀 ! Thanks @rcardin :)

[rcardin]

I'll release a new version next Monday.