This implements the upcoming draft-13
but has bits to make it work with draft-02
that most (all?) Chromium versions use.

Data and events are not going through
cowboy_stream beyond init. Since this
approach appears to work well it may
be a good idea to do the same for
Websocket over HTTP/2+ and improve
its performance.

It is now specified as >= 1.8.0 and < 3.0.0 since Cowboy
supports both Ranch 1.8.x and 2.x.