Alembic migration environment.

Create a new migration after changing ORM models:

    alembic revision --autogenerate -m "describe the change"

Apply migrations:

    alembic upgrade head

Roll back one revision:

    alembic downgrade -1

For an existing database that was created with AUTO_CREATE_SCHEMA=true and has
no alembic_version table, create a baseline stamp before using migrations:

    alembic stamp head
