Generic single-database configuration.

Before running DB migrations, ensure that the following environment variables are declared.

    - TETHYS_DB_USERNAME
    - TETHYS_DB_PASSWORD
    - TETHYS_DB_HOST
    - TETHYS_DB_NAME
    - TETHYS_DB_PORT

To create a new migration, run `alembic revision -m "some comment"`

To run the latest DB migration, run the `alembic upgrade head` command from the alembic directory.

You can also upgrade or downgrade "N" versions by running `alembic upgrade +N` or `alembic downgrade -N`
