Support for Python 3.9-3.11 in orm-migrations

[Kaplas85]

Hello. The orm-migrations branch is only available up to Python version 3.8.

The symbols library and parser are not available since 3.10 and the deprecation warning is thrown in 3.9. I am trying to make these changes but I create the issue to leave evidence of this and if someone wants to contribute.

The library since python 3.10 to replace the ones mentioned above is the ast library.

[maybephilipp]

I think it's an old branch (see: https://blog.ponyorm.org/2019/03/19/pony-orm-migrations/)

Most likely they're working on migrations on some different branch/repository. I also found an article about 0.8 version. It looks unofficial (and for some reason in Russian language), but it sounds like happy news (https://docs.ponyorm.org/upgrade_pony.html?highlight=structure)

[jwaggy]

I would also like to see migrations happen for pony.

[leosok]

I am searching for an expressive ORM for a project right now. Is someone using Pony in production? Is it still maintained?