zeroize: run clippy, clean up some docs and typos #463

Job	Run time
cross (powerpc-unknown-linux-gnu, 1.60.0)	4m 50s
build (1.60.0, armv7a-none-eabi)	4m 12s
cross (powerpc-unknown-linux-gnu, stable)	47s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.60.0, sudo apt update && sudo apt install gcc-mult...	5m 50s
build (1.60.0, thumbv7em-none-eabi)	4m 15s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	1m 1s
build (1.60.0, wasm32-unknown-unknown)	5m 12s
build (stable, armv7a-none-eabi)	8s
aarch64 (aarch64-unknown-linux-gnu, 1.60.0)	5m 53s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.60.0)	5m 4s
build (stable, thumbv7em-none-eabi)	12s
aarch64 (aarch64-unknown-linux-gnu, stable)	1m 32s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	20s
build (stable, wasm32-unknown-unknown)	17s
test (x86_64-apple-darwin, macos-latest, 1.60.0)	5m 12s
test (x86_64-apple-darwin, macos-latest, stable)	50s
test (x86_64-pc-windows-msvc, windows-latest, 1.60.0)	5m 42s
test (x86_64-pc-windows-msvc, windows-latest, stable)	1m 41s
minimal-versions / minimal-versions	1m 1s
	53m 59s

Provide feedback