* 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.
When `-- features tls` is specified for tarpc, RPC communication can
also occur over a `TlsStream<TcpStream>` instead of a `TcpStream`.
* The functional tests have been refactored to use a common set of
functions for constructing the client and server structs so that all
the tests are shared across non-tls and tls test runs.
* Update pre-push to test TLS
* The `cfg_attr` logic caused many false warnings from clippy, so for now the crate docs for TLS are not tested.
