Add --save-on-error flag, closes #626

[berleon]

Save the notebook even if an error occurs.

[takluyver]

So there's already an option --allow-errors which will continue if an error occurs. Is it important to you that you stop executing the notebook but still convert/save it afterwards? I'm slightly concerned by how many error-handling options we're growing here - it feels like there should be a simpler way.

With your new option, is the error shown in the terminal at all?

[berleon]

My use-case is that I am running some experiments in the notebook. If an error occurs, I want to see the previous outputs. However, continue running (i.e. --allow-errors) can cost unnecessary time (multiple hours).

I agree that the additional flag might make it unnecessary complicated. What would you say to unify the error handling behaviour as --on-error=[abort|continue|stop] where abort would be the current default behaviour, continue would correspond to --allow-errors and stop would mean to still save/convert the notebook but not continue with the execution.

As with --allow-errors, the error is not shown in the terminal. I could print the error to stdout and add a message that the notebook will still be converted/saved.

[ciaochiaociao]

Any update?