Implement sort() method

[maman]

Summary

This PR adds both implementations and tests for LinkedList.prototype.sort method which can be used as follows:

const list = new LinkedList(2, 1, 3);
list.sort()
// output [1, 2, 3]
list.sort((a, b) => {a.values - b.values})
// output [3, 2, 1];

The default sort method is using mergesort as per ecma262 implementation of Array.prototype.sort, but simplified.

Fixes #3

[adeyahya]

I think we should not use standard Array since the LinkedList are alternative to dynamic array, not an abstraction on top of it.

there is some example for implementing MergeSort in LinkedList
https://www.geeksforgeeks.org/merge-sort-for-linked-list/

[maman]

got it!