2.0.0

• Send and queue emails with Celery instead of with Cron.
• Drop priority headers (useless with queues).
• Storage backends to save emails in databases, file storages, etc.
• Cc and Bcc support.
• Supported versions: Python 3.83.11, Django 3.24.2, Celery 5.0~5.2.
• Migrate CI/CD from Travis to Github Actions.
• Docker Compose for external dependencies in development environment.
• Get django_yubin version programmatically.
• Update docs.