Remove Handle argument from I/O constructors (#61)

This commit removes the `Handle` argument from the following constructors

* `TcpListener::bind`
* `TcpStream::connect`
* `UdpSocket::bind`

The `Handle` argument remains on the various `*_std` constructors as they're
more low-level, but this otherwise is intended to set forth a precedent of by
default not taking `Handle` arguments and instead relying on the global
`Handle::default` return value when necesary.

examples/chat.rs

@@ -33,7 +33,6 @@ use futures::future::Executor;
 use futures::stream::{self, Stream};
 use futures_cpupool::CpuPool;
 use tokio::net::TcpListener;
-use tokio::reactor::Handle;
 use tokio_io::io;
 use tokio_io::AsyncRead;
 
@@ -42,8 +41,7 @@ fn main() {
     let addr = addr.parse().unwrap();
 
     // Create the TCP listener we'll accept connections on.
-    let handle = Handle::default();
-    let socket = TcpListener::bind(&addr, &handle).unwrap();
+    let socket = TcpListener::bind(&addr).unwrap();
     println!("Listening on: {}", addr);
 
     // This is currently a multi threaded server.