Apply many uncontroversial style fixes from Clippy.

Apply many uncontroversial style fixes from Clippy.

I ran 'cargo clippy fix', picked out the changes I didn't disagree
with, and reformatted a few overlong lines that resulted. It's a
combination of redundant clones and borrows, what Clippy considers to
be the antipattern of assert_eq!(boolean, true), and failure to use
the full vocabulary of standard methods like Option::is_none,
Result::is_ok, and the various and_then() or map() etc combinators.