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/api/basic_json/count.md

@@ -92,8 +92,7 @@ Logarithmic in the size of the JSON object.
 ## Version history
 
 1. Added in version 3.11.0.
-2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0. Fixed in version 3.13.0 to
-   consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
-   [`at`](at.md), [`value`](value.md), and other lookup functions.
+2. Added in version 1.0.0. Changed to support comparable key types in version 3.11.0. Support for keys convertible to
+   `std::string_view` added in version 3.13.0, consistently across the lookup functions.
 3. Deleted overload for integral key types added in version 3.13.0 to reject such calls at compile time instead of
    causing undefined behavior at runtime.