Add pointfree Pair to array (pairToArray) function

**Is your feature request related to a problem? Please describe.**

Most other Monads have a pointfree version of the `toArray` method.
- `List` -> `listToArray`
- `Tuple` -> `tupleToArray`

However there is no `pairToArray` function

**Describe the solution you'd like**
A `pairToArray` function

**Describe alternatives for how you do this now**

`(p) => p.toArray()`

**Code**
Do you have example code or tests in a [Repl](http://repl.it/languages/babel) for what you'd like added?

**Additional context**
Add any other context or screenshots about the feature request here.

I'm happy to give implementing this a go if the maintainers think it's worthwhile/will actually merge the changes 😄