This probably still needs a lot more work to be perfect; in particular
I'm not sure exactly which parts should be re-exported from
sqlalchemy/__init__.pyi and sqlalchemy/sql/__init__.pyi, but this
works with all the ways I can test it easily right now.
Also, while I've fixed sqlalchemy.sql, sqlalchemy.orm is still totally
broken since it tries to re-export tons of stuff that doesn't have
stubs yet.