Move axum-debug crate to workspace (#497)

* add axum-debug to workspace

* update readme

* add changes to changelog

* little docs update

* fix the gap

a tab has leaked into workspace Cargo.toml, it must be fixed

* address clippy warnings

axum-debug/README.md

@@ -0,0 +1,63 @@
+[![License](https://img.shields.io/crates/l/axum-debug)](https://choosealicense.com/licenses/mit/)
+[![Crates.io](https://img.shields.io/crates/v/axum-debug)](https://crates.io/crates/axum-debug)
+[![Docs - Stable](https://img.shields.io/crates/v/axum-debug?color=blue&label=docs)](https://docs.rs/axum-debug/)
+
+# axum-debug
+
+This is a debugging crate that provides better error messages for [`axum`]
+framework.
+
+[`axum`] is a great framework for developing web applications. But when you
+make a mistake, error messages can be really complex and long. It can take a
+long time for you to figure out what is wrong in your code. This crate provides
+utilities to generate better error messages in case you make a mistake.
+
+## Usage Example
+
+Will fail with a better error message:
+
+```rust
+use axum::{routing::get, Router};
+use axum_debug::debug_handler;
+
+#[tokio::main]
+async fn main() {
+    let app = Router::new().route("/", get(handler));
+
+    axum::Server::bind(&"0.0.0.0:3000".parse().unwrap())
+        .serve(app.into_make_service())
+        .await
+        .unwrap();
+}
+
+#[debug_handler]
+async fn handler() -> bool {
+    false
+}
+```
+
+Error message:
+
+```
+error[E0277]: the trait bound `bool: IntoResponse` is not satisfied
+  --> main.rs:xx:23
+   |
+xx | async fn handler() -> bool {
+   |                       ^^^^
+   |                       |
+   |                       the trait `IntoResponse` is not implemented for `bool`
+```
+
+## Safety
+
+This crate uses `#![forbid(unsafe_code)]` to ensure everything is implemented in 100% safe Rust.
+
+## Performance
+
+Macros in this crate have no effect when using release profile. (eg. `cargo build --release`)
+
+## License
+
+This project is licensed under the [MIT license](LICENSE).
+
+[`axum`]: https://crates.io/crates/axum