Reorganize the entire crate:

Renamed APIs

* Loop => reactor::Core
* LoopHandle => reactor::Handle
* LoopPin => reactor::Pinned
* TcpStream => net::TcpStream
* TcpListener => net::TcpListener
* UdpSocket => net::UdpSocket
* Sender => channel::Sender
* Receiver => channel::Receiver
* Timeout => reactor::Timeout
* ReadinessStream => reactor::PollEvented
* All `LoopHandle` methods to construct objects are now free functions on the
  associated types, e.g. `LoopHandle::tcp_listen` is now `TcpListener::bind`
* All APIs taking a `Handle` now take a `Handle` as the last argument
* All future-returning APIs now return concrete types instead of trait objects

Added APIs

* io::Io trait -- Read + Write + ability to poll

Removed without replacement:

* AddSource
* AddTimeout
* IoToken
* TimeoutToken

Closes #3
Closes #6

tests/timeout.rs

@@ -5,6 +5,7 @@ extern crate tokio_core;
 use std::time::{Instant, Duration};
 
 use futures::Future;
+use tokio_core::reactor::{Core, Timeout};
 
 macro_rules! t {
     ($e:expr) => (match $e {
@@ -16,9 +17,9 @@ macro_rules! t {
 #[test]
 fn smoke() {
     drop(env_logger::init());
-    let mut l = t!(tokio_core::Loop::new());
+    let mut l = t!(Core::new());
     let dur = Duration::from_millis(10);
-    let timeout = l.handle().timeout(dur).and_then(|t| t);
+    let timeout = Timeout::new(dur, &l.handle()).and_then(|t| t);
     let start = Instant::now();
     t!(l.run(timeout));
     assert!(start.elapsed() >= dur);