Alembic is a new database migrations tool, written by the author of
SQLAlchemy. A migrations tool offers the following functionality:
* Can emit ALTER statements to a database in order to change the structure
of tables and other constructs.
* Provides a system whereby "migration scripts" may be constructed; each script
indicates a particular series of steps that can "upgrade" a target database
to a new version, and optionally a series of steps that can "downgrade"
similarly, doing the same steps in reverse.
* Allows the scripts to execute in some sequential manner.
Documentation and status of Alembic is at http://readthedocs.org/docs/alembic/
