Add support for `Topic` header #40

Job	Run time
clippy	42s
format	11s
cargo-test (stable, ubuntu-latest)	1m 24s
cargo-test (stable, macos-latest)	1m 31s
cargo-test (stable, windows-latest)	12m 24s
cargo-test (beta, ubuntu-latest)	1m 40s
cargo-test (beta, macos-latest)	1m 12s
cargo-test (beta, windows-latest)	8m 23s
cargo-test (nightly, ubuntu-latest)	58s
cargo-test (nightly, macos-latest)	2m 27s
cargo-test (nightly, windows-latest)	11m 3s
	41m 55s

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