Change module structure. (#122)

* Change `client::{future, sync}, server::{future, sync}` to `future::{client, server}, sync::{client, server}`

This reflects the most common usage pattern and allows for some types to not need to be fully qualified when used together (e.g. the previously-named `client::future::Options` and `server::future::Options` can now be `client::Options` and `server::Options`).

* sync::client: create a RequestHandler struct to encapsulate logic of processing client requests.

The largest benefit is that unit testing becomes easier, e.g. testing that the request processing stops when all request senders are dropped.

* Rename Serialize error variants to make sense.

* Rename tarpc_service_ConnectFuture__ => Connect (because it's public)

* Use tokio proto's ClientProxy.

Rather than reimplement the same logic. Curiously, this commit
isn't a net loss in LOC. Oh well.

* Factor out os-specific functionality in listener() into their own fns

* Remove service-fn dep

examples/sync_server_calling_server.rs

@@ -16,8 +16,8 @@ use add::{SyncService as AddSyncService, SyncServiceExt as AddExt};
 use double::{SyncService as DoubleSyncService, SyncServiceExt as DoubleExt};
 use std::sync::mpsc;
 use std::thread;
-use tarpc::{client, server};
-use tarpc::client::sync::ClientExt as Fc;
+use tarpc::sync::{client, server};
+use tarpc::sync::client::ClientExt as Fc;
 use tarpc::util::{FirstSocketAddr, Message, Never};
 
 pub mod add {
@@ -69,7 +69,8 @@ fn main() {
     let (tx, rx) = mpsc::channel();
     thread::spawn(move || {
         let handle = AddServer.listen("localhost:0".first_socket_addr(),
-                         server::Options::default()).unwrap();
+                    server::Options::default())
+            .unwrap();
         tx.send(handle.addr()).unwrap();
         handle.run();
     });
@@ -80,7 +81,8 @@ fn main() {
     thread::spawn(move || {
         let add_client = add::SyncClient::connect(add, client::Options::default()).unwrap();
         let handle = DoubleServer::new(add_client)
-            .listen("localhost:0".first_socket_addr(), server::Options::default())
+            .listen("localhost:0".first_socket_addr(),
+                    server::Options::default())
             .unwrap();
         tx.send(handle.addr()).unwrap();
         handle.run();