Adding possibility to set websocket options

This makes it possible to set websocket request headers and other options.

To do it you have to explicitly instantiate a Tivoka\Client\Connection\WebSocket, I chose not to implement it in the connection factory since you must already know that it is a websocket.

I'd be greatful for a version bump after this, since I have packages depending on it (and not immediately removing the branch, since my package today specs dependency on dev-dev-websocket-options).