Enforce Rust Syntactic Guidelines with Rustfmt

https://github.com/ahmedcharles/rustfmt

I think that this is something we should implement in our workflow, at least sometime in the future (once the obvious issues with rustfmt are fixed) if not now.

Not sure if we want to automate this somehow.
If not, I'll file this as a reference, close the issue, and just add this to a potential CONTRIBUTING.md as a suggestion/requirement.
