Add rustdoc comparison with older version #697

Job	Run time
cargo-machete	3s
cargo-lock	7s
cargo-doc (ubuntu)	20s
cargo-fmt	21s
cargo-doc (windows)	2m 28s
cargo-miri	1m 36s
compilation-benchmarks	2m 2s
prettier	8s
cargo-doc (macos)	45s
runtime-benchmarks (args_3)	49s
taplo-fmt	6s
runtime-benchmarks (args_5)	1m 2s
test-msrv (ubuntu)	59s
runtime-benchmarks (args_10_alloc)	58s
test-msrv (windows)	2m 9s
test-stable (ubuntu)	1m 11s
runtime-benchmarks (args_10_structs)	56s
test-unstable (beta)	26s
test-msrv (macos)	59s
test-stable (windows)	4m 43s
runtime-benchmarks (args_10)	1m 5s
test-unstable (nightly)	19s
test-stable (macos)	1m 14s
runtime-benchmarks (args_20)	54s
typos	6s
version-sync	5s
website-build	18s
	26m 9s

Provide feedback