Extend snake_to_camel plugin to replace {} in the doc string with the original snake-cased ident. (#50)

* Extend snake_to_camel plugin to replace {} in the doc string with the origin snake-cased ident.

Also, track tokio-rs master.

This is really ad-hoc, undiscoverable, and unintuitive, but there's no way to programmatically create doc strings
in regular code, and I want to produce better doc strings for the associated types.

Given `fn foo_bar`:

Before: `/// The type of future returned by the function of the same name.`
After: ``/// The type of future returned by `{}`.``
    => `/// The type of future returned by foo_bar.`

* Fix some docs

* Use a helper fn on pipeline::Frame instead of handrolled match.

* Don't hide docs for ClientFuture.

It's exposed in the Connect impl of FutureService -- the tradeoff for not generating *another* item -- and hiding it breaks doc links.

* Formatting

* Rename snake_to_camel plugin => tarpc-plugins

* Update README

* Mangle a lot of names in macro expansion.

To lower the chance of any issues, prefix idents in service expansion with __tarpc_service.
In future_enum, prefix with __future_enum. The pattern is basically __macro_name_ident.

Any imported enum variant will conflict with a let binding or a function arg, so we basically
can't use any generic idents at all. Example:

    enum Req { request(..) }
    use self::Req::request;

    fn make_request(request: Request) { ... }

                    ^^^^^^^ conflict here

Additionally, suffix generated associated types with Fut to avoid conflicts with camelcased rpcs.
Why someone would do that, I don't know, but we shouldn't allow that wart.

examples/throughput.rs

@@ -4,7 +4,7 @@
 // This file may not be copied, modified, or distributed except according to those terms.
 
 #![feature(conservative_impl_trait, plugin)]
-#![plugin(snake_to_camel)]
+#![plugin(tarpc_plugins)]
 
 #[macro_use]
 extern crate lazy_static;
@@ -18,6 +18,7 @@ use std::time;
 use std::net;
 use std::thread;
 use std::io::{Read, Write, stdout};
+use futures::Future;
 use tarpc::util::Never;
 use tarpc::sync::Connect;
 
@@ -41,9 +42,9 @@ service! {
 struct Server;
 
 impl FutureService for Server {
-    type Read = futures::Finished<Arc<Vec<u8>>, Never>;
+    type ReadFut = futures::Finished<Arc<Vec<u8>>, Never>;
 
-    fn read(&self) -> Self::Read {
+    fn read(&self) -> Self::ReadFut {
         futures::finished(BUF.clone())
     }
 }
@@ -51,7 +52,7 @@ impl FutureService for Server {
 const CHUNK_SIZE: u32 = 1 << 19;
 
 fn bench_tarpc(target: u64) {
-    let handle = Server.listen("localhost:0").unwrap();
+    let handle = Server.listen("localhost:0").wait().unwrap();
     let client = SyncClient::connect(handle.local_addr()).unwrap();
     let start = time::Instant::now();
     let mut nread = 0;