Refactor server module.

In the interest of the user's attention, some ancillary APIs have been
moved to new submodules:

- server::limits contains what was previously called Throttler and
  ChannelFilter. Both of those names were very generic, when the methods
  applied by these types were very specific (and also simplistic). Renames
  have occurred:
  - ThrottlerStream => MaxRequestsPerChannel
  - Throttler => MaxRequests
  - ChannelFilter => MaxChannelsPerKey
- server::incoming contains the Incoming trait.
- server::tokio contains the tokio-specific helper types.

The 5 structs and 1 enum remaining in the base server module are all
core to the functioning of the server.

README.md

@@ -80,6 +80,7 @@ This example uses [tokio](https://tokio.rs), so add the following dependencies t
 your `Cargo.toml`:
 
 ```toml
+anyhow = "1.0"
 futures = "1.0"
 tarpc = { version = "0.26", features = ["tokio1"] }
 tokio = { version = "1.0", features = ["macros"] }
@@ -99,9 +100,8 @@ use futures::{
 };
 use tarpc::{
     client, context,
-    server::{self, Incoming},
+    server::{self, incoming::Incoming},
 };
-use std::io;
 
 // This is the service definition. It looks a lot like a trait definition.
 // It defines one RPC, hello, which takes one arg, name, and returns a String.
@@ -140,7 +140,7 @@ available behind the `tcp` feature.
 
 ```rust
 #[tokio::main]
-async fn main() -> io::Result<()> {
+async fn main() -> anyhow::Result<()> {
     let (client_transport, server_transport) = tarpc::transport::channel::unbounded();
 
     let server = server::BaseChannel::with_defaults(server_transport);

example-service/src/server.rs

@@ -17,7 +17,7 @@ use std::{
 };
 use tarpc::{
     context,
-    server::{self, Channel, Incoming},
+    server::{self, incoming::Incoming, Channel},
     tokio_serde::formats::Json,
 };
 use tokio::time;

tarpc/examples/tracing.rs

@@ -9,7 +9,7 @@ use futures::{future, prelude::*};
 use std::env;
 use tarpc::{
     client, context,
-    server::{BaseChannel, Incoming},
+    server::{incoming::Incoming, BaseChannel},
 };
 use tokio_serde::formats::Json;
 use tracing_subscriber::prelude::*;

tarpc/src/client.rs

@@ -317,8 +317,8 @@ where
             .map_err(ChannelError::Ready)
     }
 
-    fn start_send<'a>(
-        self: &'a mut Pin<&mut Self>,
+    fn start_send(
+        self: &mut Pin<&mut Self>,
         message: ClientMessage<Req>,
     ) -> Result<(), ChannelError<C::Error>> {
         self.transport_pin_mut()

tarpc/src/lib.rs

@@ -88,7 +88,7 @@
 //! };
 //! use tarpc::{
 //!     client, context,
-//!     server::{self, Incoming},
+//!     server::{self, incoming::Incoming},
 //! };
 //!
 //! // This is the service definition. It looks a lot like a trait definition.
@@ -111,7 +111,7 @@
 //! # };
 //! # use tarpc::{
 //! #     client, context,
-//! #     server::{self, Incoming},
+//! #     server::{self, incoming::Incoming},
 //! # };
 //! # // This is the service definition. It looks a lot like a trait definition.
 //! # // It defines one RPC, hello, which takes one arg, name, and returns a String.