Lens -> State integration returning the old value

- provides `LensFamily.modo` which returns the old value (as an alternative to `LensFamily.mods` which returns the new value)
- provides `LensFamily.assigno` which returns the old value (as an alternative to `LensFamily.assign` which returns the new value)
- both `modo` and `assigno` are provisional names
- both `modo` and `assigno` do not have a symbolic alias yet

I'd welcome suggestions for the final names of these new variants as well as suggestions for the symbolic aliases.