Move axum-debug into axum-macros (#724)

* Move axum-debug into axum-macros

* fix ref to axum-macros in changelog

* Apply suggestions from code review

Co-authored-by: Jonas Platte <[email protected]>

Co-authored-by: Jonas Platte <[email protected]>

axum-macros/tests/debug_handler/pass/impl_future.rs

@@ -0,0 +1,9 @@
+use axum_macros::debug_handler;
+use std::future::Future;
+
+#[debug_handler]
+fn handler() -> impl Future<Output = ()> {
+    async {}
+}
+
+fn main() {}