Add support for printing slices via print/println

With help from @aykevl.

testdata/print.go

@@ -45,4 +45,8 @@ func main() {
 
 	// print bool
 	println(true, false)
+
+	// print slice
+	println([]byte(nil))
+	println([]int(nil))
 }

testdata/print.txt

@@ -21,3 +21,5 @@ a b c
 (0:nil)
 map[2]
 true false
+[0/0]nil
+[0/0]nil