The file format for each option now features a "Example:" header that
can provide one or more examples that get rendered appropriately in the
output. All options MUST have at least one example or gen.pl complains
at build-time.
This fix also does a few other minor format and consistency cleanups.
Closes#7654
Even though it cannot fall-back to a lower HTTP version automatically. The
safer way to upgrade remains via CURLOPT_ALTSVC.
CURLOPT_H3 no longer has any bits that do anything and might be removed
before we remove the experimental label.
Updated the curl tool accordingly to use "--http3".
Closes#4197
