Prepare 0.9.0 release #138

Job	Run time
Miri	8m 8s
Format, lint, test, and audit	1m 12s
Platform tests (ubuntu-latest)	22s
no_std target build (aarch64-unknown-linux-gnu)	21s
Platform tests (windows-latest)	47s
Platform tests (macos-latest)	29s
no_std target build (wasm32-unknown-unknown)	16s
no_std target build (x86_64-unknown-freebsd)	16s
no_std target build (x86_64-unknown-linux-gnu)	15s
no_std target build (thumbv7em-none-eabihf)	20s
	12m 26s

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