docs: improve rusdoc / readme / changelog #617

Job	Run time
Build wasm	2m 8s
Run tests on Linux x86 (stable)	1m 4s
Run tests on macOS arm64 (Apple M1)	1m 25s
Run tests on Linux armv7	6m 14s
Run tests on Linux x86 (nightly)	1m 30s
Run tests on Linux arm64	6m 3s
Run tests on Linux x86 (stable, no default features)	1m 11s
Run tests on Linux x86 (nightly, no default features)	1m 34s
	21m 9s

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