Default struct member reordering for minimal size

Rule: largest members to smallest; if same size, order in source order

examples/basic.odin

@@ -6,7 +6,7 @@ print_string_to_buffer :: proc(buf: ^[]byte, s: string) {
 	// NOTE(bill): This is quite a hack
 	// TODO(bill): Should I allow the raw editing of a slice by exposing its
 	// internal members?
-	Raw_Bytes :: struct {
+	Raw_Bytes :: struct #ordered {
 		data: ^byte
 		len:  int
 		cap:  int

examples/demo.odin

@@ -1,13 +1,14 @@
 #load "basic.odin"
 
 main :: proc() {
-	Vector3 :: struct {
+	Vector4 :: struct {
 		x: i8
 		y: i32
 		z: i16
+		w: i16
 	}
 
-	v := Vector3{1, 4, 9}
+	v := Vector4{1, 4, 9, 16}
 
 	t := type_info(v)