feat(http1): Add higher-level HTTP upgrade support to Client and Server (#1563)

- Adds `Body::on_upgrade()` that returns an `OnUpgrade` future.
- Adds `hyper::upgrade` module containing types for dealing with
  upgrades.
- Adds `server::conn::Connection::with_upgrades()` method to enable
  these upgrades when using lower-level API (because of a missing
  `Send` bound on the transport generic).
- Client connections are automatically enabled.
- Optimizes request parsing, to make up for extra work to look for
  upgrade requests.
  - Returns a smaller `DecodedLength` type instead of the fatter
    `Decoder`, which should also allow a couple fewer branches.
  - Removes the `Decode::Ignore` wrapper enum, and instead ignoring
    1xx responses is handled directly in the response parsing code.

Ref #1563 

Closes #1395

Cargo.toml

@@ -29,7 +29,7 @@ iovec = "0.1"
 log = "0.4"
 net2 = { version = "0.2.32", optional = true }
 time = "0.1"
-tokio = { version = "0.1.5", optional = true }
+tokio = { version = "0.1.7", optional = true }
 tokio-executor = { version = "0.1.0", optional = true }
 tokio-io = "0.1"
 tokio-reactor = { version = "0.1", optional = true }
@@ -101,6 +101,12 @@ name = "send_file"
 path = "examples/send_file.rs"
 required-features = ["runtime"]
 
+[[example]]
+name = "upgrades"
+path = "examples/upgrades.rs"
+required-features = ["runtime"]
+
+
 [[example]]
 name = "web_api"
 path = "examples/web_api.rs"