Add the .Fx macro for specifying FreeBSD releases.
Add a bunch of missing standards to the .St macro.
Add Version 1 AT&T UNIX to .At macro
Updated the ".St -ansiC" macro to report "ISO 9899: 1990 (``ISO C'')"
You can also specify -iso9899, or -isoC. Use -ansiC-89 if you still need
the X3.159-1989 string reported.
Original author: mpp