compiler: generics - support across modules/files

examples/vweb/test_vweb_app.v

@@ -13,8 +13,8 @@ pub mut:
 }
 
 fn main() {
-	mut app := App{}
-	vweb.run(app, port)
+	app := App{}
+	vweb.run(mut app, port)
 	//vweb.run<App>(Port)
 }
 
@@ -22,7 +22,7 @@ pub fn (app mut App) init() {
 	app.vweb.handle_static('.')
 }
 
-pub fn (app mut App) json_endpoint() {
+pub fn (app & App) json_endpoint() {
 	app.vweb.json('{"a": 3}')
 }
 
@@ -34,7 +34,7 @@ pub fn (app mut App) index() {
 }
 */
 
-pub fn (app mut App) text() {
+pub fn (app & App) text() {
 	app.vweb.text('hello world')
 }