Add various entities for mailing lists in the format:

<!ENTITY a.[listname].url "&a.mailman.listinfo;/freebsd-[listname]">
<!ENTITY a.[listname] "<ulink url='&a.mailman.listinfo;/freebsd-[listname]'>FreeBSD list on some esoteric topic</ulink>">
<!ENTITY a.[listname].name "<ulink url='&a.[listname].url;'>freebsd-[listname]</ulink>">

Tested by: ceri