tokio-udp-framed

This started from a copy of UdpFramed from tokio-util with a few modifications that provides a somewhat different API:

• All UdpFramed types take a Borrow<UdpSocket> so you can pass an Arc<UdpSocket> or &UdpSocket
• There are UpdFramedRecv and UdpFramedSend types for specifically send and recv in Sink/Stream
• Because of Borrow<UdpSocket> you can't use get_mut anymore

The main benefit can be easily explained in an example:

```rust let asoc = Arc::new(UdpSocket::bind("127.0.0.1:0").await?); let bsoc = a_soc.clone();

let aaddr = asoc.localaddr()?; let baddr = bsoc.localaddr()?;

let mut a = UdpFramed::new(asoc, ByteCodec); let mut b = UdpFramed::new(bsoc, LinesCodec::new());

let msg = b"1\r\n2\r\n3\r\n".tovec(); a.send((&msg, baddr)).await?;

let msg = b"4\r\n5\r\n6\r\n".tovec(); a.send((&msg, baddr)).await?;

asserteq!(b.next().await.unwrap().unwrap(), ("1".tostring(), aaddr)); asserteq!(b.next().await.unwrap().unwrap(), ("2".tostring(), aaddr)); asserteq!(b.next().await.unwrap().unwrap(), ("3".tostring(), a_addr));

asserteq!(b.next().await.unwrap().unwrap(), ("4".tostring(), aaddr)); asserteq!(b.next().await.unwrap().unwrap(), ("5".tostring(), aaddr)); asserteq!(b.next().await.unwrap().unwrap(), ("6".tostring(), a_addr)); ```