Create New `set-row` Function to Modify Data in Migrations

I don't know if this is exactly the design you'd go with but I found there wasn't a means to add data to a table for migrations, yet, and I needed to use that functionality.

I was originally going to make insert-row and update-row functions and then noticed that 'set determines whether it ought to be an INSERT or an UPDATE so I just went with a set-row function, instead.