Make all libcurl related options use .nf (no fill) for the SYNOPSIS
section - for consistent look. roffit then renders that section using
<pre> (monospace font) in html for the website.
Extended manpage-syntax (test 1173) with a basic check for it.
Closes#8062
Extended manpage-syntax.pl (run by test 1173) to check that every man
page for a libcurl option has an EXAMPLE section that is more than two
lines. Then fixed all errors it found and added examples.
Reviewed-by: Daniel Gustafsson
Closes#7656
