Merge arrays
The Array class defines the + and - methods. But also | and & for union and intersection.
No surprises with the + method, which concatenates arrays, and -, which subtracts. | and & will also remove duplicated elements. Order of arrays are preserved.
The ^ method has not been implemented. But if necessary, you can make the symmetrical difference by hand!
Links to Ruby documentation for Array#+, Array#-, Array#| and Array#&.
