Provide attribute macro for multiple HTTP methods (#1674)

Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-web-codegen/tests/trybuild/route-duplicate-method-fail.rs

@@ -0,0 +1,15 @@
+use actix_web::*;
+
+#[route("/", method="GET", method="GET")]
+async fn index() -> impl Responder {
+    HttpResponse::Ok()
+}
+
+#[actix_web::main]
+async fn main() {
+    let srv = test::start(|| App::new().service(index));
+
+    let request = srv.get("/");
+    let response = request.send().await.unwrap();
+    assert!(response.status().is_success());
+}