Sorting Algorithms

[dlesnoff]

Add multiple sorting algorithms: insertion sort, selection sort, bubble sort, merge sort
with a file for some common tests.

I hesitate to add additional tests to illustrate the stability property of some sorts or to add the possibility to change the comparison function.
I want to keep thing simple to be as much pedagogical as possible.

[ZoomRmc]

Took a glance over. Looks great, I like the code/comment ratio (I'd spray TODO marks around those add description lines).

I think the testing scaffolding should live somewhere separately. Do you think it would be beneficial to start collecting the testing utils we can recommend to new contributors?

Also, in general, I don't like unseeded random in tests. No harm here, but they should be reproducible.

Re if verbose that you don't actually use, perhaps the checks can be swapped to when defined(debug)?