feat(all): add socket timeouts

Methods added to `Client` and `Server` to control read and write
timeouts of the underlying socket.

Keep-Alive is re-enabled by default on the server, with a default
timeout of 5 seconds.

BREAKING CHANGE: This adds 2 required methods to the `NetworkStream`
  trait, `set_read_timeout` and `set_write_timeout`. Any local
  implementations will need to add them.

Cargo.toml

@@ -47,5 +47,4 @@ env_logger = "*"
 default = ["ssl"]
 ssl = ["openssl", "cookie/secure"]
 serde-serialization = ["serde"]
-timeouts = []
-nightly = ["timeouts"]
+nightly = []