Use inotify/fswatch for file changes

[MasseGuillaume]

For example, on the status view, I need to press F5 to update the view. A file watch on the directory removing gitignore entries could notify tig to update.

[jonas]

Hi Guillaume, fswatch indeed looks like the best option for such a feature.

I will go ahead and close this as a duplicate of #301 which has a few comments about how the current "watch" mechanism is implemented.