Schema migrations are not possible in general.
Yes, you can diff two schemas and generate statements to turn one into the other. Adding columns works fine this way. Removing columns works fine.
Do you really need a library to add and remove columns? Not really. But rollback, someone will say. Schema migration libraries let you undo things. Nope. You can't rollback a drop column once it is committed, that data is gone.
What happens when you run into issues in production that you didn't have in your test/development environment?
Basically, automated schema migrations don't work. However, I guess if you haven't been through it you'll just have to learn the hard way. :)
SQL gives you a very flexible environment. You never have to break existing code to push out new features, if you are just a tiny bit careful.