Clippy, formatting, and minor fixes

[michaelkirk]

• [x] I agree to follow the project's code of conduct.

• [n/a] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

This is a grab bag of clippy and formatting nits, plus now CI will check for these things.

Some of the clippy suggestions are good, but here especially, where we're porting an existing codebase, sometimes the value of mirroring the upstream implementation overrides the value of sticking to rust idioms, so I'm pretty happy to allow clippy checks wherever it makes sense.

[michaelkirk]

I'm not sure that anyone else is really watching this repository, so I'll wait a day and then just self-merge.

Unless maybe @stonylohr or @phayes wants to take a look?

[phayes]

Looks good to me.

We should probably also add cargo test --no-default-features to the CI because of the addition of the accurate optional dependency

[michaelkirk]

Thanks @phayes

I've just now added a no-default-features build.

bors r+

[bors[bot]]

Build succeeded:

• tests