Pick relevant doc updates.
doc: fix DoxygenLayout.xml for doxygen 1.10
doc: add reference docs + index for config and env variables
doc: add some more coverage
doc: move config man pages under config/
doc: add sections to index, clarify discussion of properties
doc: disable dot graphs in API docs again
doc: some updates
doc: fix up example dependencies in meson
Use (fixed-up) Doxygen manpage output for all program & module manpages.
This also allows formatting the manual pages properly in the HTML docs.
The Markdown pages work properly only with Doxygen >= 1.9.7, older
versions put them to wrong place in the HTML docs.
Hide useless paginated indices.
Rename "Related Pages" -> "Pages".
Fix manpage brief description.
Fix file path name stripping.
Move macro listings after enums, so that they're next to functions.
Remove pwtest from docs, it's not API.
Fixup header styles.
Don't show page sections in left sidebar, it's confusing.
Rename Modules -> API Reference in sidebar.
Indicate visually the sidebar entries are collapsible.
Fix spa_pod_json grouping.
Move tools page to top level.
Fix page ordering.
Theme from doxygen-awesome-css with custom modifications based on the
pipewire.org website to use the same type of blue, grey, etc.
doxygen-awesome-css is MIT licensed, see
https://github.com/jothepro/doxygen-awesome-css
