Clean up warnings

[subversive-owl]

The crate issues quite a few warnings. Some of the unneeded identifiers could be intentional for later implementation, but at the moment it creates a lot of compiler output to sift through. Removing the warnings would also ensure the codebase is readable for humans and compilers the same way.

[drahnr]

I am for the _ addons, but it is hard to test since it depends on the backend selection which warnings are spawn.

[drahnr]

But yes, this is something definitely to be taken care of, especially to de-clutter the build process.

[subversive-owl]

that's a good point though, i really doubt rustc team want to try to untangle checking feature-conditional warnings automatically, so i doubt there's much we can do for the time being.