feat(lib): redesign API to use Futures and Tokio

There are many changes involved with this, but let's just talk about
user-facing changes.

- Creating a `Client` and `Server` now needs a Tokio `Core` event loop
to attach to.
- `Request` and `Response` both no longer implement the
`std::io::{Read,Write}` traits, but instead represent their bodies as a
`futures::Stream` of items, where each item is a `Chunk`.
- The `Client.request` method now takes a `Request`, instead of being
used as a builder, and returns a `Future` that resolves to `Response`.
- The `Handler` trait for servers is no more, and instead the Tokio
`Service` trait is used. This allows interoperability with generic
middleware.

BREAKING CHANGE: A big sweeping set of breaking changes.

src/http/h1/mod.rs

@@ -1,21 +1,3 @@
-/*
-use std::fmt;
-use std::io::{self, Write};
-use std::marker::PhantomData;
-use std::sync::mpsc;
-
-use url::Url;
-use tick;
-use time::now_utc;
-
-use header::{self, Headers};
-use http::{self, conn};
-use method::Method;
-use net::{Fresh, Streaming};
-use status::StatusCode;
-use version::HttpVersion;
-*/
-
 pub use self::decode::Decoder;
 pub use self::encode::Encoder;
 
@@ -23,7 +5,7 @@ pub use self::parse::parse;
 
 mod decode;
 mod encode;
-mod parse;
+pub mod parse;
 
 /*
 fn should_have_response_body(method: &Method, status: u16) -> bool {