Simplest possible sort impl

This ist the simplest possible sort implementation I found (the one in libc++ is too optimized). 
It allows to at least try the sort interface.

Test using default comparison are provided.

TODO:
- test using iterators, custom comparisons, and projections.
- test file needs cleaning.
And here: 
```c++
reverse(c);
is_sorted(sort(swap_ranges(take(c, size/2), drop(c, size/2))))
```