Add inotify support to monitor/update state #270

I am interested in that in particular somehow in interconnection with -o option so I could run ncdu as a "service" where it would react to changes (inotify) and update the du status so I could query it at any point.

There might be a use case for inotify to auto-refresh the directory while browsing, but implementing that in a way that isn't jarring may be a challenge, and it honestly doesn't seem worth the effort to me.

Writing out a full export on every change as you suggest is far too inefficient to be useful in most cases. You can script around tools like inotifywait(1) if you really want to do that anyway.