expose current task/progress

[meandavejustice]

Would be nice to have access to the current task. For my use case, I would like to be able to access
it on error so I can have some insight into which task failed. Would possibly be useful to be able to access this for tracking progress as well.

Not sure how this would be exposed outside of the case of an error. The current 'data' event emits output from stdout, which seems appropriate.

(this was discussed in #dat)