Demonstrate `columnar` stuff #580

Job	Run time
test mdBook	45s
cargo test on ubuntu, rust stable	33s
cargo test on ubuntu, rust 1.78	23s
cargo test on macos, rust stable	39s
cargo test on macos, rust 1.78	35s
cargo test on windows, rust stable	1m 26s
cargo test on windows, rust 1.78	50s
	5m 11s

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