Online AudioContext improvements (continue playing after drop, terminate event loop)

[orottier]

Fixes #464 #421

[b-ma]

Looks good to me!

Just one question, what is the use case you envision for #464 ?

[orottier]

Not a use case per se, but I think it is just a better representation of the spec.
A use case could be that this simply works:

fn play_background(buffer: AudioBuffer) {
    let context = AudioContext::default();
    let mut src = context.create_buffer_source();
    src.connect(&context.destination());
    src.set_loop(true);
    src.set_buffer(buffer);
    src.start();
}

Or do you think it is better to keep the previous behaviour?

[b-ma]

Or do you think it is better to keep the previous behaviour?

I dont know actually, no strong opinion... I don't really understand why someone would do that but I don't think this hurts neither :)