Fix for python-attrs/attrs#253 breaking change

[mjdunn]

As reported in #12, python-attrs/attrs#253 currently breaks compatibility with attrs 17.3+. This commit resets "this" attributes back onto class bodies, preserving functionality.

This commit passes all test_attrs_sqlalchemy tests.

[rouge8]

Thanks for this. Internally, we've stopped using attrs_sqlalchemy in new code. #10 realized that using attrs for hashing was a bad idea. Using attrs for __eq__ is also not great and we should let SQLAlchemy do that itself based on identity. At that point, all attrs_sqlalchemy provides is a nice __repr__ and there's probably much nicer ways to do that than pulling in attrs.

I'll leave this open for now.

[rouge8]

Hi @mjdunn, we're going ahead and deprecating attrs_sqlalchemy and do not recommend using it going foward (#14).