Feature rollup (#129)

* Create a directory for the `future::server` module, which has become quite large. server.rs => server/mod.rs. Server submodules for shutdown and connection logic are added.

* Add fn thread_pool(...) to sync::server::Options

* Configure idle threads to expire after one minute

* Add tarpc::util::lazy for lazily executing functions. Similar to `futures::lazy` but useful in different circumstances. Specifically, `futures::lazy` typically requires a closure, whereas `util::lazy` kind of deconstructs a closure into its function and args.

* Remove some unstable features, and `cfg(plugin)` only in tests. Features `unboxed_closures` and `fn_traits` are removed by replacing manual Fn impls with Stream impls. This actually leads to slightly more performant code, as well, because some `Rc`s could be removed.

* Fix tokio deprecation warnings. Update to use tokio-io in lieu of deprecated tokio-core items. impl AsyncRead's optional `unsafe fn prepare_uninitialized_buffer` for huge perf wins

* Add debug impls to all public items and add `deny(missing_debug_implementations)` to the crate.

* Bump tokio core version.

examples/readme_sync.rs

@@ -27,7 +27,7 @@ struct HelloServer;
 
 impl SyncService for HelloServer {
     fn hello(&self, name: String) -> Result<String, Never> {
-        Ok(format!("Hello, {}!", name))
+        Ok(format!("Hello from thread {}, {}!", thread::current().name().unwrap(), name))
     }
 }