Add support for `Topic` header #41

Job	Run time
clippy	1m 10s
format	4s
cargo-test (stable, ubuntu-latest)	47s
cargo-test (stable, macos-latest)	1m 23s
cargo-test (stable, windows-latest)	12m 15s
cargo-test (beta, ubuntu-latest)	1m 54s
cargo-test (beta, macos-latest)	1m 37s
cargo-test (beta, windows-latest)	12m 16s
cargo-test (nightly, ubuntu-latest)	1m 24s
cargo-test (nightly, macos-latest)	1m 15s
cargo-test (nightly, windows-latest)	8m 9s
	42m 14s

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