Implement ncal features

[b1rger]

• -h Turns off highlighting of today.
• -J Display Julian Calendar, if combined with the -o option, display date of Orthodox Easter according to the Julian Calendar.
• -e Display date of Easter (for western churches).
• -j Display Julian days (days one-based, numbered from January 1).
• -m month Display the specified month. If month is specified as a decimal number, appending ‘f’ or ‘p’ displays the same month of the following or previous year respectively.
• -o Display date of Orthodox Easter (Greek and Russian Orthodox Churches).
• -p Print the country codes and switching days from Julian to Gregorian Calendar as they are assumed by ncal. The country code as determined from the local environment is marked with an asterisk.
• -s country_code Assume the switch from Julian to Gregorian Calendar at the date associated with the country_code. If not specified, ncal tries to guess the switch date from the local environment or falls back to September 2, 1752. This was when Great Britain and her colonies switched to the Gregorian Calendar.
• -w Print the number of the week below each week column.
• -y Display a calendar for the specified year. This option is implied when a year but no month are specified on the command line.
• -3 Display the previous, current and next month surrounding today.
• -1 Display only the current month. This is the default.
• -A number Months to add after. The specified number of months is added to the end of the display. This is in addition to any date range selected by the -y, -3, or -1 options. For example, “cal -y -B2 -A2” shows everything from November of the previous year to February of the following year. Negative numbers are allowed, in which case the specified number of months is subtracted. For example, “cal -y -B-6” shows July to December. And “cal -A11” simply shows the next 12 months.
• -B number Months to add before. The specified number of months is added to the beginning of the display. See -A for examples.
• -C Completely switch to cal mode. For cal like output only, use -b instead.
• -d yyyy-mm Use yyyy-mm as the current date (for debugging of date selection).
• -H yyyy-mm-dd Use yyyy-mm-dd as the current date (for debugging of highlighting).
• -M Weeks start on Monday.
• -S Weeks start on Sunday.
• -W number First week of the year has at least number days.
• -b Use oldstyle format for ncal output.

See also https://manpages.debian.org/bullseye/ncal/ncal.1.en.html