Alow Mutating Entry keys and iterator keys #361

Job	Run time
clippy	18s
miri	3m 40s
tests (1.63.0)	1m 21s
nostd_build (1.63.0, thumbv6m-none-eabi)	35s
tests (stable, arbitrary)	53s
nostd_build (stable, thumbv6m-none-eabi)	9s
tests (stable, quickcheck)	40s
Check MSRV and minimal-versions	1m 6s
tests (stable, rayon)	46s
tests (stable, rustc-rayon)	45s
tests (stable, serde)	45s
tests (stable, borsh)	35s
tests (stable, std)	39s
tests (beta)	36s
tests (nightly, test build benchmarks)	43s
Success	1s
	13m 32s

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