Django-Firebird changes : 2.2a1 released

Django-Firebird changes : The stable version corresponds with django 2.2 and lives into stable/2.2.x branch. The current master branch of this repository is being developed under django 3.0.x.

django-firebird 2.2a1 is also published to pypi https://pypi.org/project/django-firebird/2.2a1/