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`.

examples/client.rs

@@ -5,7 +5,7 @@ extern crate http;
 extern crate io_dump;
 extern crate tokio_core;
 
-use h2::client::{Client};
+use h2::client;
 use h2::RecvStream;
 
 use futures::*;
@@ -55,7 +55,7 @@ pub fn main() {
 
     let tcp = tcp.then(|res| {
         let tcp = io_dump::Dump::to_stdout(res.unwrap());
-        Client::handshake(tcp)
+        client::handshake(tcp)
     }).then(|res| {
             let (mut client, h2) = res.unwrap();