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/src/lib.rs

@@ -0,0 +1,104 @@
+//! 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.
+//!
+//! While using [`axum`], you can get long error messages for simple mistakes. For example:
+//!
+//! ```rust,compile_fail
+//! use axum::{routing::get, Router};
+//!
+//! #[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();
+//! }
+//!
+//! fn handler() -> &'static str {
+//!     "Hello, world"
+//! }
+//! ```
+//!
+//! You will get a long error message about function not implementing [`Handler`] trait. But why
+//! this function does not implement it? To figure it out [`debug_handler`] macro can be used.
+//!
+//! ```rust,compile_fail
+//! # 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]
+//! fn handler() -> &'static str {
+//!     "Hello, world"
+//! }
+//! ```
+//!
+//! ```text
+//! error: handlers must be async functions
+//!   --> main.rs:xx:1
+//!    |
+//! xx | fn handler() -> &'static str {
+//!    | ^^
+//! ```
+//!
+//! As the error message says, handler function needs to be async.
+//!
+//! ```rust,compile_fail
+//! 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() -> &'static str {
+//!     "Hello, world"
+//! }
+//! ```
+//!
+//! # Performance
+//!
+//! Macros in this crate have no effect when using release profile. (eg. `cargo build --release`)
+//!
+//! [`axum`]: axum
+//! [`Handler`]: axum::handler::Handler
+//! [`debug_handler`]: debug_handler
+
+#![warn(
+    clippy::all,
+    clippy::dbg_macro,
+    clippy::todo,
+    clippy::mem_forget,
+    rust_2018_idioms,
+    future_incompatible,
+    nonstandard_style,
+    missing_debug_implementations,
+    missing_docs
+)]
+#![deny(unreachable_pub, private_in_public)]
+#![forbid(unsafe_code)]
+
+pub use axum;
+pub use axum_debug_macros::debug_handler;