The file list_test.cc contains a program that allows the user
to test the sort function of a linked list. For this assignment write the
MergeSort function. The function should sort a list in ascending order
using the specified callback function. It should sort the list in-place,
that is, it should not allocate a second list or array to help with sorting.
Be sure to test your code on multiple examples and on the cs server.
Tar your code in a file that contains your name and submit it on course Inquire site.