Just four comments:
1 - Good work
2 - It might be better to leave FN_QUICKSORT alone inside libSort.sqf, taking the "custom" comparison functions outside that module. The custom comparison functions, as examples, might be defined just inside init.sqf.
3 - You may use a TAG to name that function as well as libSort.sqf. If you dont have one, your may register yours here
4 - As another example of the versatility of your function, you might add an example with a custom comparison function where an array of units is sorted based on the side, for example, west, east, civilian, resistance, or based on type: man, tank, car, air, or distances to a point, etc, I mean something different than just a typical numerical or alphanumerical sorting.