Add all of the possible errno's to example.3.
Show examples of the .Bx (BSD) and .At (AT&T UNIX) macros
in the various HISTORY sections.
Add some .Rs/.Re (used for referencing things other
than man pages) in the SEE ALSO sections.
Suggested by: wollman
since it seemed like a better place, and the makefiles for
/usr/share/examples didn't need to be fussed with.
The old stuff can be removed from the Attic.