examples: add sum example (its not pretty)

examples/sum/sum_test.go

@@ -0,0 +1,20 @@
+package sum
+
+import (
+	"testing"
+	"testing/quick"
+)
+
+//go:generate go run asm.go -out sum.s -stubs stub.go
+
+func expect(xs []uint64) uint64 {
+	var s uint64
+	for _, x := range xs {
+		s += x
+	}
+	return s
+}
+
+func TestSum(t *testing.T) {
+	quick.CheckEqual(Sum, expect, nil)
+}