* Introduce IntoResponseHeaders trait
* Implement IntoResponseHeaders for HeaderMap
* Add impl IntoResponse for impl IntoResponseHeaders
… and update IntoResponse impls that use HeaderMap to be generic instead.
* Add impl IntoResponseHeaders for Headers
… and remove IntoResponse impls that use it.
* axum-debug: Fix grammar in docs
* Explain confusing error message in docs
* Move `IntoResponse` to axum-core
* Move `FromRequest` to axum-core
* some clean up
* Remove hyper dependency from axum-core
* Fix docs reference
* Use default
* Update changelog
* Remove mention of default type
* Make `axum-debug` handle more cases
* Only just trybuild tests on stable
* revert changes to hello-world example
* Remove a bit of duplication
* return error on generics
* address review feedback
* Support associated functions with receiver or returns `Self`
* fix indentation