Introduce Response type alias as a shorthand for Response<BoxBody> (#590)

* Introduce `Response` type alias as a shorthand

* Don't re-export `Response` at the crate root

examples/versioning/src/main.rs

@@ -6,10 +6,9 @@
 
 use axum::{
     async_trait,
-    body::BoxBody,
     extract::{FromRequest, Path, RequestParts},
-    http::{Response, StatusCode},
-    response::IntoResponse,
+    http::StatusCode,
+    response::{IntoResponse, Response},
     routing::get,
     Router,
 };
@@ -51,7 +50,7 @@ impl<B> FromRequest<B> for Version
 where
     B: Send,
 {
-    type Rejection = Response<BoxBody>;
+    type Rejection = Response;
 
     async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
         let params = Path::<HashMap<String, String>>::from_request(req)