This is still the very same approach (in the way the array is split
and how elements are compared). The only difference is that the
recursive implementation is replaced by a non-recursive one.
It's (still) stable, top-down merge-sort.
The non-recursive implementation better, because it avoids the overhead
of the function call to recurse.
Add a stable, recursive merge sort for CList.
This could be improved by doing an iterative implementation.
The recursive implementation's stack depth is not an issue,
as it is bound by O(ln(n)). But an iterative implementation
would safe the overhead of O(n*log(n)) function calls and be
potentially faster.
