generate docs for feature gated items (#1332)

* generate docs for feature-gated items on crates.io

* add newline in Cargo.toml

* unify newlines

* fix clippy

* introduce macros for features

* commit missing file

* Update subxt/src/lib.rs

* make it compile

subxt/src/backend/rpc/mod.rs

@@ -56,8 +56,9 @@
 // with other file names for their types.
 #![allow(clippy::module_inception)]
 
-#[cfg(feature = "jsonrpsee")]
-mod jsonrpsee_impl;
+crate::macros::cfg_jsonrpsee! {
+    mod jsonrpsee_impl;
+}
 
 mod rpc_client;
 mod rpc_client_t;

subxt/src/backend/rpc/rpc_client.rs

@@ -19,6 +19,7 @@ pub struct RpcClient {
 
 impl RpcClient {
     #[cfg(feature = "jsonrpsee")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "jsonrpsee")))]
     /// Create a default RPC client pointed at some URL, currently based on [`jsonrpsee`].
     ///
     /// Errors if an insecure URL is provided. In this case, use [`RpcClient::from_insecure_url`] instead.