rpc: expose http, websocket under client

Re-export client::transport::{http, websocket} (guarded by appropriate
feature gates) publicly under the client module.
This is to expose the Builder types defined in each of the modules
as public API, with properly built documentation.

rpc/src/client.rs

@@ -15,10 +15,10 @@ pub mod sync;
 mod transport;
 
 #[cfg(feature = "http-client")]
-pub use transport::http::{HttpClient, HttpClientUrl};
+pub use transport::http::{self, HttpClient, HttpClientUrl};
 #[cfg(feature = "websocket-client")]
 pub use transport::websocket::{
-    WebSocketClient, WebSocketClientDriver, WebSocketClientUrl, WebSocketConfig,
+    self, WebSocketClient, WebSocketClientDriver, WebSocketClientUrl, WebSocketConfig,
 };
 
 #[cfg(any(feature = "http-client", feature = "websocket-client"))]