generate .str() for all arrays

compiler/tests/str_gen_test.v

@@ -0,0 +1,16 @@
+struct Foo {
+	a int 
+} 
+
+fn test_array_str() {
+	f := Foo{34}
+	println(f) 
+	//s := f.str() 
+	//println(s) 
+	n := [i64(1), 2, 3] 
+	assert n.str() == '[1, 2, 3]' 
+	println(n)  // make sure the array is printable 
+	n2 := [4,5,6] 
+	assert n2.str() == '[4, 5, 6]' 
+	println(n2) 
+}