Prepare 0.10.4 release; DashIterator doc #419

Job	Run time
cargo fmt	8s
cargo test msrv	4m 39s
Docs (macOS-latest)	47s
cargo test nightly (macOS-latest)	40s
Docs (windows-2019)	2m 10s
Docs (ubuntu-latest)	26s
cargo test nightly (windows-2019)	1m 17s
cargo clippy+test (wasm32) (macOS-latest)	1m 6s
cargo test nightly (ubuntu-latest)	37s
cargo clippy+test (macOS-latest)	1m 16s
cargo clippy+test (wasm32) (windows-2019)	2m 36s
cargo clippy+test (windows-2019)	3m 36s
cargo clippy+test (wasm32) (ubuntu-latest)	53s
cargo clippy+test (ubuntu-latest)	1m 17s
	21m 28s

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