Type in the subdeck method from the alternate
version of Chapter 13, and test it.
Using the pseudocode in Chapter 13,
write the method called merge.
Write the simple version of mergeSort, the one
that divides the deck in half and then uses sortDeck
to sort the two halves. Then it uses merge to create a new,
Note that in previous assignments when we ``broke'' arrays
in half, we just used index ranges to specify the halves.
We didn't actually create halves. For mergeSort we
actually create new decks and subdecks using subdeck