You want to create your own driver? You don't need to directly contribute to the project. You can require them directly in the database.json config.
There are two ways, to use your own drivers.
You can create a driver and make it available for everyone, by publishing it via npm.
You need to follow the name convention
You don't need to publish your driver, instead see the non global configuration at the features
You need to inherit from the following interface, or at least you need to provide all functions available.
To require the base driver, you need to do the following:
$ npm install umigrate-db-basedriver --save
After this you can require this base driver and inherit from it via
Example database driver
The default driver is the perfect way for you to start developing your own driver.
You can find the driver here.