Add freeifaddrs to the NAME section

Remove workaround for ancient HTML generation code.

Add ifa_addrflags to ifaddrs.

branches: 1.16.2;
unsigned -> unsigned int

Update synopses to match u_int/u_long/etc. changes. Do not bump date as
it's not a substantive change.

Remove trailing whitespace.

Add a small example.

branches: 1.12.6; 1.12.12;
Use .In for header files instead of .Ar Pa and variations.

Mark up NULL. New sentence, new line. Bump date for previous.

For non-AF_LINK ifaddrs, ifa_data is NULL. AFAICT, this has always been
so. Say so in the documentation.

Fix preamble

branches: 1.8.38; 1.8.42; 1.8.46;
Use
.In header.h
instead of
.Fd #include \*[Lt]header.h\*[Gt]
Much easier to read and write, and supported by groff for ages.
Okayed by ross.

Generate <>& symbolically.

Sort sections, sort SEE ALSO, and misc. fixes.

Boring whitespace fixes.

Fix date.

branches: 1.3.2;
Use .{B,Bs,F,N,O}x and fix miscellaneous errors.

add freeifaddrs(), which reclaims region allocated by getifaddrs().
in sync with kame and bsdi.

add getifaddrs(3) from bsdi4, as mentioned in tech-net (in SIOCGIFCONF
related thread).
this will save future apps from complexity of SIOCGIFCONF.

getifaddrs(3) does not use SIOCGIFCONF internally, it uses sysctl.