Filesystem.Monitor: use System.FSEvents or System.Inotify to provide low overhead
NOTE: I originally envisioned something much more elegant, however when I started
down that path, I quickly realized that I don't really understand how the Monitor really
works. This code appears to work properly, however someone who understands it better
should probably take a closer look.
Feel free to use this as a guide for what needs to be done when solving the problem properly.