Improve documentation: byte layouts, release pages, See also, dark-mode images (#5906)

- Make the iterator range illustrations legible in dark mode (prefers-color-scheme
  rules inside the SVGs).
- Add a "Byte layout" section with a color-coded byte table to each binary format
  page (BJData, BON8, BSON, CBOR, MessagePack, UBJSON), and highlight the smallest
  size per file in the comparison table.
- Add "See also" sections to the overview pages that lacked one.
- Split the release notes into one page per release, grouped by minor version on
  the overview page, with an "API changes" section per release generated from the
  API pages' version histories (hooks/api_changes.py).
- Fact-check the release notes and version histories against the release tags and
  correct wrong or misleading entries (e.g., json_serializer 2.1.0, merge_patch
  3.1.0, items, count, operator[], to_bjdata, std::string_view key support).

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

docs/mkdocs/docs/index.md

@@ -92,7 +92,7 @@ Conda, and more), and pkg-config.
 
     What changed in each release, with links to the relevant documentation.
 
-    [:octicons-arrow-right-24: Releases](home/releases.md)
+    [:octicons-arrow-right-24: Releases](home/releases/index.md)
 
 -   :octicons-people-24:{ .lg .middle } __Community__
 
@@ -108,7 +108,7 @@ Conda, and more), and pkg-config.
 
     This documentation is built from the `develop` branch and may describe changes that are not part of a release
     yet. Their version numbers are followed by an <span class="unreleased-version">unreleased</span> badge; see
-    [Releases](home/releases.md) for what shipped in each version.
+    [Releases](home/releases/index.md) for what shipped in each version.
 
 The library is licensed under the [MIT License](home/license.md). The source code, issue tracker, and discussions
 are on [GitHub](https://github.com/nlohmann/json).