added support for creating custom methods with route macro (#2969)

Co-authored-by: Rob Ede <robjtede@icloud.com>
Closes https://github.com/actix/actix-web/issues/2893

actix-web-codegen/tests/trybuild/route-custom-lowercase.rs

@@ -0,0 +1,19 @@
+use actix_web_codegen::*;
+use actix_web::http::Method;
+use std::str::FromStr;
+
+#[route("/", method = "hello")]
+async fn index() -> String {
+    "Hello World!".to_owned()
+}
+
+#[actix_web::main]
+async fn main() {
+    use actix_web::App;
+
+    let srv = actix_test::start(|| App::new().service(index));
+
+    let request = srv.request(Method::from_str("hello").unwrap(), srv.url("/"));
+    let response = request.send().await.unwrap();
+    assert!(response.status().is_success());
+}