The flatten method on Array squishes any nested
arrays into the outer array like this:
> [[1,2],[3,[4,5]]].flatten
=> [1, 2, 3, 4, 5]The object of this exercise is to recreate the functionality of the
flatten method that we have in Ruby's Array class.
Implement a CustomArray class that works like this:
> c = CustomArray.new([[1,2],[3,[4,5]]])
> c.flatten
=> [1, 2, 3, 4, 5]But the CustomArray class may not use the
built-in .flatten method or .to_s