'ProxySorter' should be able to sort array slices

It is currently not possible to sort a slice of an array with the `ProxySorter` class.
```java
public static <T> int[] sort(
    final T array,
    final int fromIndex, // Inclusively
    final int toIndex,   // Exlusively
    final Comparator<? super T> comparator
); 
```