Re-work I/O

* Auto-register interest whenever we see WouldBlock
* Remove implementations of `Stream<Item=Ready>`, no longer needed
* Add explicit `poll_{read,write}` methods, if needed
* Remove all I/O streams, libstd ones suffice
* Update all I/O futures

tests/echo.rs

@@ -3,13 +3,14 @@ extern crate futures;
 extern crate futures_io;
 extern crate futures_mio;
 
-use std::net::TcpStream;
+use std::io::{self, Read, Write};
+use std::sync::Arc;
 use std::thread;
-use std::io::{Read, Write};
 
 use futures::Future;
 use futures::stream::Stream;
-use futures_io::{copy, TaskIo};
+use futures_io::copy;
+use futures_mio::TcpStream;
 
 macro_rules! t {
     ($e:expr) => (match $e {
@@ -29,6 +30,8 @@ fn echo_server() {
 
     let msg = "foo bar baz";
     let t = thread::spawn(move || {
+        use std::net::TcpStream;
+
         let mut s = TcpStream::connect(&addr).unwrap();
 
         for _i in 0..1024 {
@@ -41,7 +44,10 @@ fn echo_server() {
 
     let clients = srv.incoming();
     let client = clients.into_future().map(|e| e.0.unwrap()).map_err(|e| e.0);
-    let halves = client.and_then(|s| TaskIo::new(s.0)).map(|i| i.split());
+    let halves = client.map(|s| {
+        let s = Arc::new(s.0);
+        (SocketIo(s.clone()), SocketIo(s))
+    });
     let copied = halves.and_then(|(a, b)| copy(a, b));
 
     let amt = t!(l.run(copied));
@@ -49,3 +55,21 @@ fn echo_server() {
 
     assert_eq!(amt, msg.len() as u64 * 1024);
 }
+
+struct SocketIo(Arc<TcpStream>);
+
+impl Read for SocketIo {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        (&*self.0).read(buf)
+    }
+}
+
+impl Write for SocketIo {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        (&*self.0).write(buf)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        (&*self.0).flush()
+    }
+}