- Prevents empty notification emails from being sent
- Hooks to WP's post update and rewrite post notification logic
- Prevents scheduling multiple queues of the same newsletter
- Fixes issue with segments not updating when scheduling a newsletter
- Removes depreciated hash field & associated logic
- Simplifies cron status message
- Implements newsletter change detection between scheduled queues
- Implements detection for subscribers who unsubscribed from list
- Implements detection for WP users who changed roles
- Updates scheduler worker logic
- Various fixes
