nub
===

Return all the unique elements of an array. You can specify your own uniqueness
comparison function with `nub.by` too.

These work like haskell's `nub` and `nubBy` functions in Data.List.

methods
=======

nub(xs)
-------

Return a new array with all the uniqe elements in `xs`.

Uniqueness is calculated `===` style so the types matter.

nub.by(xs, cmp)
---------------

Use `cmp(x,y)` function to compare elements instead of the default.
`cmp` should return whether the two elements are equal as a boolean.