Make JSON and HTTP1 support optional (#286)

* Make json support an optional feature

* Fix Json type documentation

* Make hyper's http1 feature optional

src/extract/mod.rs

@@ -192,6 +192,7 @@ pub use self::{
     request_parts::{BodyStream, RawBody},
 };
 #[doc(no_inline)]
+#[cfg(feature = "json")]
 pub use crate::Json;
 
 #[cfg(feature = "multipart")]

src/extract/rejection.rs

@@ -25,9 +25,11 @@ define_rejection! {
     pub struct HeadersAlreadyExtracted;
 }
 
+#[cfg(feature = "json")]
 define_rejection! {
     #[status = BAD_REQUEST]
     #[body = "Failed to parse the request body as JSON"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
     /// Rejection type for [`Json`](super::Json).
     pub struct InvalidJsonBody(Error);
 }
@@ -199,11 +201,13 @@ composite_rejection! {
     }
 }
 
+#[cfg(feature = "json")]
 composite_rejection! {
     /// Rejection used for [`Json`](super::Json).
     ///
     /// Contains one variant for each way the [`Json`](super::Json) extractor
     /// can fail.
+    #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
     pub enum JsonRejection {
         InvalidJsonBody,
         MissingJsonContentType,