cal: add support for highlighting an arbitrary date

cal: add support for highlighting an arbitrary date

This is done by calling cal with the extra day parameter like:

cal 14 9 1752

Note the tests were updated to use the new syntax.

Note also that this patch changes the -y option
to always print a full year, even if a month or
the -[13] options are specified.
This matches the cal operation from bsdmainutils on debian
and also allows one to print a full year while
highlighting a particular date.

Signed-off-by: Pádraig Brady <P@draigBrady.com>