CHANGES:

- Hierarchical documentation (@jonludlam, @panglesd, @Julow)
  Pages can now be organized in a directory tree structure.
  Relative and absolute references are added:
  `{!./other_page.label}`, `{!//other_page}`.

- Improved sidebar and breadcrumbs navigation (@panglesd, @gpetiot)
  The documentation pages and the libraries of the entire package are shown on
  the left sidebar.

- Added support for images, videos, audio and other assets
  The syntax is `{image!/reference/to/asset}` or `{image:URL}` for images.
  The syntax for `{video...}` and `{audio...}` is the same.
  (@panglesd, @EmileTrotignon, ocaml/odoc#1170, ocaml/odoc#1171, ocaml/odoc#1184, ocaml/odoc#1185)

- Search using Sherlodoc (@panglesd, @EmileTrotignon, @Julow)
  A new search bar that supports full-text and type-based search.

- Experimental driver (@jonludlam, @panglesd)
  The driver builds the documentation for a collection of Opam packages using
  the newer Odoc features. It supports linking external packages to ocaml.org
  and markdown files.
  This is experimental and will break in the future.

- Cross-package references (@panglesd, @Julow)
  Pages and modules from other packages can be referenced:
  `{!/otherpackage/page}`, `{!/otherpackage/Module.t}`.

- Option to remap links to other packages to ocaml.org or other site.
  See the `--remap` option of the driver or the `--remap-file` option of `odoc html-generate`.
  (@jonludlam, ocaml/odoc#1189, ocaml/odoc#1248)

- Option to compute occurrences of use of each identifiers
  The commands `aggregate-occurrences` and `count-occurrences` are added.
  (@panglesd, ocaml/odoc#976, ocaml/odoc#1076, ocaml/odoc#1206)

- Added the `odoc classify` command (@jonludlam, ocaml/odoc#1121)
  Helps driver detecting which modules belong to which libraries.
- Added `--suppress-warnings` to the CLI to remove warnings from a unit, even
  if they end up being raised in another unit through expansion
  (@jonludlam, ocaml/odoc#1260)
- Add clock emoji before `@since` tag (@yawaramin, ocaml/odoc#1089)
- Navigation for the search bar : use '/' to enter search, up and down arrows to
  select a result, and enter to follow the selected link. (@EmileTrotignon, ocaml/odoc#1088)
- Fix a big gap between the preamble and the content of a page (@EmileTrotignon, ocaml/odoc#1147)
- Add a marshalled search index consumable by sherlodoc (@EmileTrotignon, @panglesd, ocaml/odoc#1084)
- Allow referencing of polymorphic constructors in polymorphic variant type
  aliases (@panglesd, ocaml/odoc#1115)
- Added a home icon in the breacrumbs (@panglesd, ocaml/odoc#1251)
  It can be disabled with a CLI option.
- Add a frontmatter syntax for mld pages (@panglesd, ocaml/odoc#1187, ocaml/odoc#1193, ocaml/odoc#1243, ocaml/odoc#1246, ocaml/odoc#1251)
  Allows to specify the title of a page, the order of sub-pages and other
  behaviors in the sidebar.
- Added `odoc-md` to process standalone Markdown pages (@jonludlam, ocaml/odoc#1234)

- The command line interface changed to support the new features.
  + Packages and libraries: `odoc link` must now be aware of packages and
    libraries with the `-L libname:path` and `-P pkgname:path` options. The
    module search path should still be passed with the `-I` option.
    The current package should be specified with `--current-package=pkgname`.
  + Hierarchy: `odoc compile` now outputs `.odoc` in the directory tree
    specified with `--output-dir=DIR` and the parent identifier must be
    specified with `--parent-id=PARENT`.
    The option `--source-parent-file` is removed.
  + Source code: Implementations are compiled with `compile-impl` instead of
    with `compile`. The options `--cmt=..` and `--source-name=..` are removed.
    Source code pages are generated with `html-generate-source`.
  + Assets: The commands `compile-asset`, `html-generate-asset` are added.
    The option `html-generate --asset` is removed.
  + Sidebar: The index is built using `compile-index`. The sidebar data is
    extracted from the index with `sidebar-generate` and passed to
    `html-generate --sidebar=..`.

- The syntax for `@tag` is now delimited (@panglesd, ocaml/odoc#1239)
  A `@tag` can now be followed by a paragraph or other elements.

- Updated colors for code fragments (@EmileTrotignon, ocaml/odoc#1023)
- Fixed complexity of looking up `.odoc` files (@panglesd, ocaml/odoc#1075)
- Normalize whitespaces in codespans (@gpetiot, ocaml/odoc#1085)
  A newline followed by any whitespaces is normalized as one space character.
- Reduce size of `Odoc_html_frontend` when compiled to javascript
  (@EmileTrotignon, ocaml/odoc#1072)
- Overhaul of module-type-of expansions and shadowing code (@jonludlam, ocaml/odoc#1081)
- Output file paths and labels in the man and latex backends changed to avoid
  name clashes (@Julow, ocaml/odoc#1191)

- Fix variant constructors being hidden if they contain hidden types
  (@jonludlam, ocaml/odoc#1105)
- Fix rare assertion failure due to optional parameters
  (@jonludlam, ocaml/odoc#1272, issue ocaml/odoc#1001)
- Fix resolution of module synopses in {!modules} lists that require --open
  (@jonludlam, ocaml/odoc#1104}
- Fix top comment not being taken from includes often enough (@panglesd, ocaml/odoc#1117)
- Fixed 404 links from search results (@panglesd, ocaml/odoc#1108)
- Fixed title content not being picked up across pages when rendering references
  (ocaml/odoc#1116, @panglesd)
- Fix wrong links to standalone comments in search results (ocaml/odoc#1118, @panglesd)
- Remove duplicated or unwanted comments with inline includes (@Julow, ocaml/odoc#1133)
- Fix bug where source rendering would cause odoc to fail completely if it
  encounters invalid syntax (@jonludlam ocaml/odoc#1208)
- Add missing parentheses in 'val (let*) : ...' (@Julow, ocaml/odoc#1268)
- Fix syntax highlighting not working for very large files
  (@jonludlam, @Julow, ocaml/odoc#1277)

- odoc-md doesn't contain tests, so don't try to run any
- odoc has a soft dependency on yojson, so it's happy to compile without it.
  However, when it is present, it does try to compile the sub-libraries that
  and they require yojson > 1.6.0