This CI library provides a simple way to bring datastructures into Codeigniter v3 to get you started migrating a legacy project.
In your Codeigniter app simply setup your database connection then:
$this->load->libary('BootstrapMigrations');
$version = '001';
$this->BootstrapMigrations->create_migration($version);
And the library will output a file to the /application/migrations folder named "001_BootstrapMigrations.php" ready for use with the built-in Codeigniter migrations class (https://www.codeigniter.com/user_guide/libraries/migration.html).
If you find a bug or have a feature request open up an issue and I'll see if I can help.