This one took a little bit of tracking down; the VfsWatcher used to spawn a new
thread and then stall/park forever. With one of the recent changes to get rid of
the extra thread, VfsWatcher started getting dropped, which in turn dropped the
watchers created by the notify crate.
Because the threads only tie back to the VfsWatcher was a cloned
Arc<Mutex<VfsSession>>, everything was fine, except that their mpsc::Receiver
objects were no longer receiving events.
This manifested itself as the file watcher magically not watching any files.
Oops.
* Moved commands into their own folder to reduce `bin.rs`'s size
* Moved all of the VFS-related functionality into its own folder
* Documented a lot of functions, including a few very obscure ones
