Fix documentation of cross product; add convenience Vec2 methods #744

Job	Run time
formatting	23s
cargo clippy (windows-latest)	1m 7s
cargo clippy (macos-latest)	38s
cargo check (msrv) (wasm32)	23s
cargo check (msrv) (windows-latest)	51s
cargo clippy (ubuntu-latest)	42s
cargo clippy (wasm32)	40s
cargo check (msrv) (macos-latest)	29s
cargo check (msrv) (ubuntu-latest)	28s
cargo doc	17s
cargo test (windows-latest)	46s
cargo test (wasm32)	22s
cargo test (macos-latest)	26s
typos	4s
cargo test (ubuntu-latest)	21s
	7m 57s

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