Prepare 0.10.4 release; DashIterator doc #420

Job	Run time
cargo fmt	14s
cargo test msrv	5m 25s
Docs (macOS-latest)	47s
cargo test nightly (macOS-latest)	38s
Docs (windows-2019)	2m 32s
cargo test nightly (windows-2019)	1m 11s
Docs (ubuntu-latest)	23s
cargo clippy+test (macOS-latest)	1m 26s
cargo test nightly (ubuntu-latest)	40s
cargo clippy+test (wasm32) (macOS-latest)	1m 22s
cargo clippy+test (windows-2019)	1m 53s
cargo clippy+test (wasm32) (windows-2019)	2m 44s
cargo clippy+test (ubuntu-latest)	57s
cargo clippy+test (wasm32) (ubuntu-latest)	1m 8s
	21m 20s

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