Remove statement that inet_pton() extends inet_ntoa();

Remove statement that inet_pton() extends inet_ntoa();
that's not really true, since inet_pton() doesn't support
all of the string forms that are supported by inet_ntoa();
as per http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=482987.
Describe IPv6 address formats.
Describe dotted decimal format in more detail.
Add an example program.
Remove unneeded header files from SYNOPSIS.
Make NAME line more precise.
Make description of return value more precise.
SEE ALSO: Add inet(3), Add getaddrinfo(3).