Support for Manual Migrations

Migrated issue, originally created by Glen Fletcher

I'm not sure whether this is a problem with the documentation or the code. However I suspect its the documentation that is at fault.

The Documentation, only talks about automatic migration using change scripts, however this isn't always an suitable for a problem.

I would like to see a clearly defined may of manually altering a specific database, lets say I have a Database connection through SQLAlchemy, open on an interactive console. I then want to be able run commands like those used in the change scripts to alter the database. I can't find how to achieve this in the documentation. It should be possible since the framework is effectively doing that but it is designed to work from the migration environment rather than explaining how to open the connection from an interactive session, and setup the state so I can run the requited commands to alter the database.

Such functivity is important for plugin based projects where plugins may require extra columns or tables in the database, it this case there is no linear series of versions, as every instance of the application will have different plugins and therefore different database migrations.

Please update the documentation to cover such usage (and if necessary update the code to provide necessary support)

Start by reviewing the documentation for automatic migrations, change scripts, and the migration environment, then compare it with the SQLAlchemy interactive-console workflow described here. Define what manual database changes and migration state must be documented, and verify that the resulting guidance covers plugin-specific schemas without a linear migration history.