Update to latest mdbook and mdbook-mermaid

[jonathanpallant]

Please check output carefully. Ideally diff the HTML output to see what has changed.

[miguelraz]

I did a good visual inspection and a git diff --no-index _newbook book yields only changes to the scrollbox, which I think we can ignore.

I also get a

Warning: The mdbook-mermaid preprocessor was built against version 0.4.28 of mdbook, but we're being called from version 0.4.36

output in the console when building which I didn't know how to get rid of.

I don't think it's a blocker, so I'm approving.

[jonathanpallant]

cargo install mdbook-mermaid will, I think, update your mermaid plugin for mdbook.