Add stop button

[Pharap]

Currently there's no way to stop the embedded emulator once it's running without refreshing the page.
Adding a stop button would be useful for stopping the game whilst writing code or doing other things (e.g. checking documentation).

[felipemanga]

Currently you can stop the emulator by pressing esc.

Still, it would be good to have something in the UI. Maybe change the play button into a stop button while the emulator is running?

[Pharap]

I didn't know about the esc button, I haven't found it documented anywhere.
That's useful to know.

Maybe change the play button into a stop button while the emulator is running?

This is roughly what I was thinking.

A red button with a black square to signal that "this is stop, not pause".

Though I was thinking that the button should be separate from the play button to prevent it being pressed twice by accident.
Maybe that's not an issue though?