Simplify markup for inline code to plain .Li in most places.

Use backslashes to protetect embedded spaces in inline code to prevent
filling from stretching them.

Use .Fn and .Fa to refer only to things this manual page documents,
they are not to be used for "a function" or "a function argument" in
general.

In code examples drop the empty line at the beginning of a function
(mandated by the KNF when there are no variables) - it doesn't help
readability here.

(uwe)