cal: Mark the current day as inverted text

...instead of putting a star `*` next to it. This makes `cal`s output
much prettier, and gets rid of one FIXME. :^)

Don't use the escape sequence from the deleted FIXME - \e[30;47m would
set the background to white and foreground to black - which presumably
wouldn't do much on a light-theme terminal. Instead use \e[7m which sets
the color as "inverted".

Base/usr/share/man/man1/cal.md

@@ -13,6 +13,8 @@ $ cal [[month] year]
 This program displays a simple calendar. If no arguments are specified, the current month is displayed with the current day highlighted.
 An overview of a whole year is displayed when a `year` is passed without a `month`.
 
+The current day is always highlighted.
+
 Days, months and years are specified with numbers. Week starts at Sunday.
 
 ## Examples

Userland/Utilities/cal.cpp

@@ -13,6 +13,9 @@
 #include <LibMain/Main.h>
 #include <time.h>
 
+#define ANSI_INVERT_OUTPUT "\e[7m"
+#define ANSI_RESET_OUTPUT "\e[0m"
+
 int const line_width = 70;
 int const line_count = 8;
 int const column_width = 22;
@@ -41,9 +44,7 @@ static ErrorOr<Vector<String>> month_lines_to_print(int month, int year)
             row.append("   "sv);
         } else {
             if (year == current_year && month == current_month && day_to_print == current_day) {
-                // FIXME: To replicate Unix cal it would be better to use "\x1b[30;47m%2d\x1b[0m " in here instead of *.
-                //        However, doing that messes up the layout.
-                row.appendff("{:02}*", day_to_print);
+                row.appendff(ANSI_INVERT_OUTPUT "{:02}" ANSI_RESET_OUTPUT " ", day_to_print);
             } else {
                 row.appendff("{:02} ", day_to_print);
             }