(WIP) refine the token constructors:

- for invocation, reorder the parameters for a more "natural language" mental model
- for delegation, make "subject" a required parameter to avoid make powerline by mistake
- for delegation, implement powerline

token/invocation/examples_test.go

@@ -27,7 +27,7 @@ func ExampleNew() {
 		return
 	}
 
-	inv, err := invocation.New(iss, sub, cmd, prf,
+	inv, err := invocation.New(iss, cmd, sub, prf,
 		invocation.WithArgument("uri", args["uri"]),
 		invocation.WithArgument("headers", args["headers"]),
 		invocation.WithArgument("payload", args["payload"]),