Misc renames (#202)

This patch renames a number of types and functions making
the API more consistent.

* `Server` -> `Connection`
* `Client` -> `SendRequest`
* `Respond` -> `SendResponse`.

It also moves the handshake fns off of `Connection` and make
them free fns in the module. And `Connection::builder` is removed
in favor of `Builder::new`.

tests/codec_write.rs

@@ -27,7 +27,7 @@ fn write_continuation_frames() {
         )
         .close();
 
-    let client = Client::handshake(io)
+    let client = client::handshake(io)
         .expect("handshake")
         .and_then(|(mut client, conn)| {
             let mut request = Request::builder();