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/udp-codec.rs

@@ -18,7 +18,6 @@ use futures::{Future, Stream, Sink};
 use futures::future::Executor;
 use futures_cpupool::CpuPool;
 use tokio::net::{UdpSocket, UdpCodec};
-use tokio::reactor::Handle;
 
 pub struct LineCodec;
 
@@ -39,15 +38,13 @@ impl UdpCodec for LineCodec {
 fn main() {
     drop(env_logger::init());
 
-    let handle = Handle::default();
-
     let pool = CpuPool::new(1);
 
     let addr: SocketAddr = "127.0.0.1:0".parse().unwrap();
 
     // Bind both our sockets and then figure out what ports we got.
-    let a = UdpSocket::bind(&addr, &handle).unwrap();
-    let b = UdpSocket::bind(&addr, &handle).unwrap();
+    let a = UdpSocket::bind(&addr).unwrap();
+    let b = UdpSocket::bind(&addr).unwrap();
     let b_addr = b.local_addr().unwrap();
 
     // We're parsing each socket with the `LineCodec` defined above, and then we