algo: Add more benchmark cases.

A quick overview shows that quicksort is indeed performing best for average
(random) input.

	BenchmarkQuickSortRand4k       5000     704413 ns/op     5.81 MB/s
	BenchmarkSelSortRand4k          100   18990390 ns/op     0.22 MB/s
	BenchmarkInsSortRand4k           50   52660694 ns/op     0.08 MB/s
	BenchmarkBubbleSortRand4k        20   85731437 ns/op     0.05 MB/s