Give feedback as to when the code is running

[mr-nano]

Since there is some delay in seeing the output of the code, it might be useful to give a visual indiction as to when the code is executing or when its done executing. If you think its a good idea, I can try coming up with some mockups.

[lostfields]

sure, that could be nice. not sure how it should be displayed though

[tomprogers]

I don't know what capabilities you have as an extension author, but perhaps you could change the styling of the buffer tab. Maybe make it pulse once each time the buffer is processed.