feat(client): add connect, read, and write timeouts to client

[hjr3]

• Add a TimeoutConnector implememtation that can be used to wrap any
  implemention of Connect.
• Add read and write timeout support to Client and client Config.
  The internal client implementation now wraps I/O with the
  tokio-io-timeout crate. Due to the way tokio-proto works, the user
  will see a "broken pipe" error instead of a "timed out" error when
  a read or write timeout occurs.

Closes #1234

• The commit messages match the guidelines in https://github.com/hyperium/hyper/blob/master/CONTRIBUTING.md#git-commit-guidelines

[seanmonstar]

It looks like this can work entirely out-of-crate? I kind of lean towards keeping it that way. Is there something that having this in crate allows that wouldn't be possible otherwise?

As a side note, looking at the tokio-io-timeout crate, the implementations of AsyncRead and AsyncWrite don't pass forward the read_buf and write_buf methods, which would mean readv and writev are no longer used for TcpStream.

[hjr3]

@seanmonstar TimeoutConnector can be out of crate. I don't see how the read and write timeouts would be out of crate. That being said, I was looking at other issues where you were talking about the ClientProto onion. Maybe that is a better way to introduce some of this functionality.

[seanmonstar]

Can't the read and write timeouts be set in any connector by returning a TimeoutStream?

[hjr3]

Of course! Not sure why I did not think of that earlier. Ok, I will make a separate crate and add all of the logic there.