Add Serial Window Ctrl-C ("Break") button to go with the Ctrl-D ("Restart") button

[Timeline8]

Put it right here...

Makes it easy to restart your code with the Restart button and then with little movement of the mouse be hovering over and ready to hit the "Break" (Ctrl-C) button while watching your code as we often need to do.

The "Break" name is just an example so whatever you think is the most appropriate name for Ctrl-C (break, interrupt, stop, etc.) is fine with me.

[dhalbert]

There is actually literally UART "break" support, if I remember right, so something like "Stop" would be better, I think.