More functionality in individual migrations

[isokissa]

Sometimes it's not enough to have migrations with SQL (DDL), especially if you have to run some sort of migration/data-conversion scripts that are written as dart function.

It would be useful to allow that migrations are not just SQL but also dart functions.

[esarbanis]

That's a cool idea! I need to find time for this, but if you have time feel free to open a PR, just let me know 🙂

[isokissa]

It would be fun to contribute, especially because it's not urgent :) You can add me as a contributor, @esarbanis