Create make target to ensure that all Rust files have been formatted with rustfmt
We should have a CI task that ensures Rust files have been properly formatted- this will be helpful when reviewing PRs.
Other linting tooling can be added here in the future (for example, any clippy warnings we want to explicitly check) but starting with rustfmt seems like a good first step.
It looks like running rustfmt with
--check will be helpful here: https://github.com/rust-lang-nursery/rustfmt#running