Configure SQLAlchemy for projects without flask

I discourage you to use an ORM to manage the interactions with the database. Check the alternative solutions.

Install Alembic:
```
pip install alembic
```
It's important that the migration scripts are saved with the rest of the source code. Following Miguel Gringberg suggestion, we'll store them in the {{ program_name }}/migrations directory.

Execute the following command to initialize the alembic repository.
```
alembic init {{ program_name }}/migrations
```

Create the basic models.py file under the project code.

"""
Module to store the models.

Classes:
    Class_name: Class description.
    ...
"""

import os

from sqlalchemy import \
    create_engine, \
    Column, \
    Integer
from sqlalchemy.ext.declarative import declarative_base

db_path = os.path.expanduser('{{ path_to_sqlite_file }}')
engine = create_engine(
    os.environ.get('{{ program_name }}_DATABASE_URL') or 'sqlite:///' + db_path
)

Base = declarative_base(bind=engine)

class User(Base):
    """
    Class to define the User model.
    """
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True, doc='User ID')

Create the migrations/env.py file as specified in the alembic article.

Create the first alembic revision.

alembic \
    -c {{ program_name }}/migrations/alembic.ini \
    revision \
    --autogenerate \
    -m "Initial schema"

Set up the testing environment for SQLAlchemy