feat: allow optionally ignoring specific paths

[DanielCodesphere]

I have only tried this using inotify and nodejs, but it seems to work and is very useful in my case. There are probably lot's of things missing to make this work with other backends and tests, but i don't know this watcher or c well enough to do that properly. If FAN_MARK_FILESYSTEM is going to be supported in the future, then filtering paths has to be done differently for that as well.

[e-dant]

Overall this looks good.

I do worry about incompatibilities between platforms, and other platform-dependent behavior, though.