Slice: find v2 (#17)

* If slice len is zero then return false
* Convert find to generic form.
* If return T is nil then no items matched the predicate func

slice/slice_test.go

@@ -220,7 +220,7 @@ func TestFind(t *testing.T) {
 		t.Fatal("found nothing")
 	}
 
-	if res != 2 {
+	if *res != 2 {
 		internal.LogFailedTestInfo(t, "Find", nums, 2, res)
 		t.FailNow()
 	}