It can be rather surprising when new lints pop up when a new stable
toolchain is released. Let's pin this check to a specific version to
avoid those surprises.
Might as well run the lints on our tests and examples. When I first
started doing this cleanup, I thought this was the default, but I must
have run `cargo clippy --all-targets` at some point in there.
Dario Nieuwenhuis
Alex Crawford
Adam Greig