Running `cargo fmt`

[jtracey]

Rustfmt (i.e., cargo fmt) is the de facto standard for formatting rust code, to the point that a lot of rust editors are configured to run it on save by default (see e.g. Jon Gjengset's videos for an example of what that looks like). It looks like this repo has either never been formatted with it, or it's been a long time. Would you accept a PR that runs cargo fmt, then cleans up edge cases like strings and comments?