This commit sponsored by Jessica Howard. Thanks, sistah!
older codebases can have their databases updated to the new structure
when they run `./bin/gmg dbupdate`.
+The first time `./bin/gmg dbupdate` is run by a user, it creates the
+tables at the current state that they're defined in models.py and sets
+the migration number to the current migration... after all, migrations
+only exist to get things to the current state of the db. After that,
+every migration is run with dbupdate.
+
There's a few things you need to know:
- We use `sqlalchemy-migrate