Change HeaderMap extractor to clone the headers (#698)

* Change `HeaderMap` extractor to clone the headers

* fix docs

* changelog

* inline variable

* also add changelog item to axum

* don't list types from axum in axum-core's changelog

* document that `HeaderMap::from_request` clones the headers

* fix typo

* a few more typos

examples/customize-extractor-error/src/main.rs

@@ -73,9 +73,6 @@ where
                     JsonRejection::MissingJsonContentType(err) => {
                         (StatusCode::BAD_REQUEST, err.to_string().into())
                     }
-                    JsonRejection::HeadersAlreadyExtracted(err) => {
-                        (StatusCode::INTERNAL_SERVER_ERROR, err.to_string().into())
-                    }
                     err => (
                         StatusCode::INTERNAL_SERVER_ERROR,
                         format!("Unknown internal error: {}", err).into(),