Add `CHANGELOG.md` #499

Job	Run time
cargo fmt	12s
cargo test nightly (macOS-latest)	37s
cargo test msrv	1m 8s
cargo test nightly (windows-2019)	57s
Docs (macOS-latest)	17s
cargo test nightly (ubuntu-latest)	23s
cargo clippy+test (macOS-latest)	32s
Docs (windows-2019)	1m 37s
cargo clippy+test (windows-2019)	2m 31s
Docs (ubuntu-latest)	13s
cargo clippy+test (wasm32) (macOS-latest)	25s
cargo clippy+test (ubuntu-latest)	39s
cargo clippy+test (wasm32) (windows-2019)	2m 26s
cargo clippy+test (wasm32) (ubuntu-latest)	35s
	12m 32s

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