The public headers saw lots of cleanups, backporting from SDL3 docs, and
merging with the wiki.
The markdown files in docs/README-*.md were converted to Unix endlines.
Otherwise, the API documentation will encode the home directory of the
user or autobuilder that built SDL, instead of telling the user to use
the literal string $(HOME) as intended.
See also <https://github.com/doxygen/doxygen/issues/7073>.
Signed-off-by: Simon McVittie <smcv@debian.org>
