Support sorting of primitive lists by indirect comparison.

[vmzakharov]

The proposal is to add the following APIs on PrimitiveLists (in addition to the existing sortThis()):

• PrimitiveList sortThis(PrimitiveComparator comparator)
• <T> PrimitiveList sortThisBy(PrimitiveFunction<T> keyExtractor) // sorts by the natural order of the keys
• <T> PrimitiveList sortThisBy(PrimitiveFunction<T> keyExtractor, Comparator<? super T> keyComparator)

Where PrimitiveComparator is a Single Abstract Method interface that looks like

public interface PrimitiveComparator
{
    int compare(primitive value1, primitive value2);
}

To support this a new sort implementation will be required.

[nikhilnanivadekar]

This looks fine as a starting point. Please raise a PR. Thanks!