Automatic WS server API

[xaviervia]

While Websockets are used more oftenly in the context of Web Apps where an HTTP server is already available, node-jstp users will benefit for getting an API for node-jstp to start the HTTP by itself if a port number, and not an HTTP server, is provided.

jstp.listen({
  ws: 8000
});

[xaviervia]

Also: afterwards, the user should be able to get the initialized HTTP server