- Add title to Table of Contents (add `on_this_page` i18n)
- Add back to top link in Table of Contents (add `back_to_top` i18n)
- Enable custom HTML in Table of Contents
(create `layouts/partials/docs_toc_foot.html`)
- Revised alert shortcode style
- Enable icons as menu items in main navbar (use HTML in `Name` field)
- Enable `[[menu.main_right]]` options for having both left and right
aligned main menu links
