Move FromRequest and IntoResponse into new axum-core crate (#564)

* 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

axum-core/src/extract/tuple.rs

@@ -0,0 +1,40 @@
+use super::{FromRequest, RequestParts};
+use crate::{body::BoxBody, response::IntoResponse};
+use async_trait::async_trait;
+use http::Response;
+use std::convert::Infallible;
+
+#[async_trait]
+impl<B> FromRequest<B> for ()
+where
+    B: Send,
+{
+    type Rejection = Infallible;
+
+    async fn from_request(_: &mut RequestParts<B>) -> Result<(), Self::Rejection> {
+        Ok(())
+    }
+}
+
+macro_rules! impl_from_request {
+    () => {};
+
+    ( $($ty:ident),* $(,)? ) => {
+        #[async_trait]
+        #[allow(non_snake_case)]
+        impl<B, $($ty,)*> FromRequest<B> for ($($ty,)*)
+        where
+            $( $ty: FromRequest<B> + Send, )*
+            B: Send,
+        {
+            type Rejection = Response<BoxBody>;
+
+            async fn from_request(req: &mut RequestParts<B>) -> Result<Self, Self::Rejection> {
+                $( let $ty = $ty::from_request(req).await.map_err(|err| err.into_response())?; )*
+                Ok(($($ty,)*))
+            }
+        }
+    };
+}
+
+all_the_tuples!(impl_from_request);