feat(client): add a new Client struct with super powers

- Includes ergonomic traits like IntoUrl and IntoBody, allowing easy
usage.
- Client can have a RedirectPolicy.
- Client can have a SslVerifier.

Updated benchmarks for client. (Disabled rust-http client bench since it
hangs.)

src/client/response.rs

@@ -38,7 +38,7 @@ impl Response {
         debug!("{} {}", version, status);
 
         let headers = try!(header::Headers::from_raw(&mut stream));
-        debug!("{}", headers);
+        debug!("Headers: [\n{}]", headers);
 
         let body = if headers.has::<TransferEncoding>() {
             match headers.get::<TransferEncoding>() {