cargo-modify

currently a proof of concept for being able to switch the new resolver on via a cmd line call during a CI build job:

```sh

remove 'resolver' from Cargo.toml

cargo modify --new-resolver=false

set new resolver

cargo modify --new-resolver=true

as above, this is the default

cargo modify ```

Caution this will reorder your Cargo.toml arbitrarily. Primary use-case is to do on-the-fly changes on a CI

later we could use this to allow arbitrary edits on a Cargo.toml