Benchmark test for the imperative SumLoop function

We have heard that recursion in Go can be slow. So, let's write some benchmark tests to check it out. First, let's test the performance of the basic imperative function SumLoop:

func benchmarkSumLoop(s []int, b *testing.B) {
       for n := 0; n < b.N; n++ {
              SumLoop(s)
       }
}

func BenchmarkSumLoop40(b *testing.B) { benchmarkSumLoop([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40}, b) }

Results: It took 46.1 ns/op.