Breaking changes
* Nuntius does not depend on celery anymore, and the old way of sending emails through celery tasks is gone. It means
that the old `NUNTIUS_CELERY_BROKER` setting is obsolete.
Features
* Nuntius now has a dedicated worker command that will start up a process responsible for sending campaigns. That
process starts up several processes to send emails and is much faster. See the documentation on how to configure.