Fewer deadlocks

• BSD/macOS: Fix possible deadlock on closing the watcher on kqueue (thanks @nhooyr and @glycerine)
• Tests: Fix missing verb on format string (thanks @rchiossi)
• Linux: Fix deadlock in Remove (thanks @aarondl)
• Linux: Watch.Add improvements (avoid race, fix consistency, reduce garbage) (thanks @twpayne)
• Docs: Moved FAQ into the README (thanks @vahe)
• Linux: Properly handle inotify's IN_Q_OVERFLOW event (thanks @zeldovich)
• Docs: replace references to OS X with macOS