Cockroach DB backend for Django 2.2

This is an initial attempt at a backend for Django 2.2. You can install it with the following command:

pip install .

You then can use this by putting the following in your settings.py for your site:

DATABASES = {
    'default': {
        'NAME': 'django',
        'USER': 'root',
        'PASSWORD': '',
        'HOST': 'localhost',
        'PORT': '26257',
        'ENGINE': 'cockroach.django',
    }
}