docs: address review comments on the new design

- Home: add a "Latest release" button
- Sponsors: update the list and group it by tier
- Features: list all feature pages on the index page
- Releases: add highlights per release, link the 4.0 roadmap, add the first commit to the timeline
- Exceptions: prefix all example messages with the exception name
- API: no code font for format names in the See also links of the to_/from_ pages
- Merge Patch: show the document before, the patch, and the result
- Replace "--" with typographic dashes, mark external links with an icon, center Mermaid diagrams

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/overrides/home.html

@@ -11,6 +11,7 @@
         <p class="nj-hero__actions">
           <a href="{{ 'integration/' | url }}" class="md-button md-button--primary nj-hero__button">Get started</a>
           <a href="{{ 'api/basic_json/' | url }}" class="md-button nj-hero__button">API documentation</a>
+          <a href="{{ 'home/releases/v3.12.0/' | url }}" class="md-button nj-hero__button">Latest release</a>
         </p>
       </div>
       <div class="nj-hero__code" aria-hidden="true">