Support for hijacking the socket

[halorgium]

Sooo, rack now has hijack support.
And I thought it might be interesting to put this on the client side.

Being able to get a handle on the raw client socket would allow for a similar advantage for WebSockets etc.

/cc @benburkert @mkb @jacobo

[benburkert]

Sounds like a cool idea. It would be nice if you could add a "protocol upgrade detection" middleware to the stack that hijacks the socket when websockets, http 2.0, or whatever is initiated by the server. Although the client code for those different protocols falls outside the scope of this library.

[halorgium]

It would be possible to use https://github.com/faye/websocket-protocol-ruby for the WebSocket part.