Add -w (watch) option.

[qm3ster]

This would also require adding output to file functionality,
since you have to overwrite the output file again and again.
I might implement this myself, submitting the issue to see if such a thing would be accepted.

[RobLoach]

Watch could likely be offloaded to something like npm I watch.

[RobLoach]

Or in here. Not sure what the best design is. I'm open for either!

[qm3ster]

I think it makes sense here, because it's a manually invoked cli for short temporary tasks, and as I have seen so far everything that wraps will require more configuration. Plus, performance reasons.