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.

tests/drop-core.rs

@@ -2,6 +2,7 @@ extern crate tokio;
 extern crate futures;
 
 use std::thread;
+use std::net;
 
 use futures::future;
 use futures::prelude::*;
@@ -13,7 +14,9 @@ use tokio::reactor::Reactor;
 fn tcp_doesnt_block() {
     let core = Reactor::new().unwrap();
     let handle = core.handle();
-    let listener = TcpListener::bind(&"127.0.0.1:0".parse().unwrap(), &handle).unwrap();
+    let listener = net::TcpListener::bind("127.0.0.1:0").unwrap();
+    let addr = listener.local_addr().unwrap();
+    let listener = TcpListener::from_std(listener, &addr, &handle).unwrap();
     drop(core);
     assert!(listener.incoming().wait().next().unwrap().is_err());
 }
@@ -22,7 +25,9 @@ fn tcp_doesnt_block() {
 fn drop_wakes() {
     let core = Reactor::new().unwrap();
     let handle = core.handle();
-    let listener = TcpListener::bind(&"127.0.0.1:0".parse().unwrap(), &handle).unwrap();
+    let listener = net::TcpListener::bind("127.0.0.1:0").unwrap();
+    let addr = listener.local_addr().unwrap();
+    let listener = TcpListener::from_std(listener, &addr, &handle).unwrap();
     let (tx, rx) = oneshot::channel::<()>();
     let t = thread::spawn(move || {
         let incoming = listener.incoming();