Update output on source change (update on a keypress or update on save)

[sajjadG]

output can't be updated after a change to the source code (I'm using python). ctrl+b doesn't recognize the last output and opens another output. if it recognizes the current output and just updates it, it would be better. and if an option for update on save be added to the extension it would be so much better.

[rwinzhang]

@sajjadG do you mean there are multiple output panel? check this pull request #9.