Add store_attributes

Closes #19 
It would appear that `Attribute` should use `attributes` or at least some of the functions, assuming that's possible without circularity (I think it probably should be?) but I didn't feel like doing that refactor right now, so I left that. Also, I intentionally left out `init_aliaser` from the comparison, because it doesn't seem relevant for comparison and because it seems like what you get out of `_ensure_attributes` constructing an `Attribute` is different than the default for that for some reason (which failed the test).