v0.4.0

Feature:

• ♻️ Add WatcherPool cleaner process: this is a process that is triggered on Notification related events to kill watchers that are not claimed anymore by any Notification resource.
• 🏳️ Add flag --enable-watcher-cleaner to enable WatcherPool cleaner process. This is disabled by default while it's experimental feature
• 📜 Update README to include changes

Contributors:
@achetronic