parser: disallow statements after a return, branch check $if, $else, switch, and loops correctly

vlib/vweb/tmpl/tmpl.v

@@ -17,13 +17,11 @@ pub fn compile_template(path string) string {
 	//lines := os.read_lines(path)
 	mut html := os.read_file(path) or {
 		panic('html failed')
-		return ''
 	} 
 	mut	header := ''
 	if os.file_exists('header.html') { 
 		h := os.read_file('header.html') or {
 			panic('html failed')
-			return ''
 		} 
 		header = h.replace('\'', '"') 
 	} 

vlib/vweb/vweb.v

@@ -85,13 +85,12 @@ $html
 
 pub fn run<T>(port int) { 
 	println('Running vweb app on http://localhost:$port ...') 
-	l := net.listen(port) or { panic('failed to listen') return } 
+	l := net.listen(port) or { panic('failed to listen') } 
 	mut app := T{} 
 	app.init() 
 	for {
 		conn := l.accept() or {
 			panic('accept() failed') 
-			return 
 		} 
 		// TODO move this to handle_conn<T>(conn, app)
 		s := conn.read_line()