Change JS to use internal options

[Martinomagnifico]

I would like to move the tracking ID to be in the internal options object. The same goes for the debug. I set that one to be an option as well, so users don't need to add the script tag for debugging. The custom event is then also no longer needed, because the object is only called when debug is set to true. I also changed the readme a bit to reflect the changed options.