Website style changed

The site theme has been changed to Abridge for Zola. Some graphical details and features are missing, and may be re-added, like the paginator on the post page. As a bonus, Abridge is actively developed and accepting contributions.

• Wide-screen setups get to see an index (or TOC) listings next to the page.
• The current setup defaults to dark mode, which can be toggled in the top-right corner (with JavaScript enabled; it stores theme:"light" in the local browser storage)
• Privacy info was added