Completed initial implementation of parallel sort.  It uses an in-place ...

...merge sort implemented with parallel block exchange.  The time limit isn't set up yet, but all the parallel algorithms are cancellable.
@bsoetaer 
Couple problems here I think:
* @start is not referenced so this will modify non-slice elements potentially ie range = 0..5 and @start = 5
* Even if @start is included, if range.min + array.length is greater than @end then values beyond the slice will be modified