improve doc, remove unused code #33

Job	Run time
clippy	14s
Test 1.60 on ubuntu-latest ()	4m 4s
rustfmt	19s
Test 1.60 on ubuntu-latest (--no-default-features)	4m 0s
Test stable on ubuntu-latest ()	22s
Test 1.60 on macos-latest ()	1m 8s
Test stable on ubuntu-latest (--no-default-features)	17s
Test 1.60 on macos-latest (--no-default-features)	1m 11s
Test nightly on ubuntu-latest ()	19s
Test 1.60 on windows-latest ()	5m 1s
Test nightly on ubuntu-latest (--no-default-features)	17s
Test 1.60 on windows-latest (--no-default-features)	5m 7s
Test stable on macos-latest ()	42s
Test stable on macos-latest (--no-default-features)	45s
Test nightly on macos-latest ()	34s
Test nightly on macos-latest (--no-default-features)	3m 0s
Test stable on windows-latest ()	48s
Test stable on windows-latest (--no-default-features)	42s
Test nightly on windows-latest ()	37s
Test nightly on windows-latest (--no-default-features)	35s
	30m 2s

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