Swap Handle/Pinned

* Handle -> Remote
* Pinned -> Handle

All APIs now take a `&Handle` by default and in general can return an immediate
`io::Result` instead of an `IoFuture`. This reflects how most usage will likely
be done through handles rather than remotes, and also all previous functionality
can be recovered with a `oneshot` plus `Remote::spawn`.

Closes #15

src/net/mod.rs

@@ -7,5 +7,5 @@ mod tcp;
 mod udp;
 
 pub use self::tcp::{TcpStream, TcpStreamNew};
-pub use self::tcp::{TcpListener, TcpListenerNew, Incoming};
+pub use self::tcp::{TcpListener, Incoming};
 pub use self::udp::{UdpSocket, UdpSocketNew};