Add table heading and footnote support

Closes #116

src/Spectre.Console/Extensions/CalendarExtensions.cs

@@ -79,5 +79,22 @@ namespace Spectre.Console
             calendar.HightlightStyle = style ?? Style.Plain;
             return calendar;
         }
+
+        /// <summary>
+        /// Sets the calendar's header <see cref="Style"/>.
+        /// </summary>
+        /// <param name="calendar">The calendar.</param>
+        /// <param name="style">The header style.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static Calendar SetHeaderStyle(this Calendar calendar, Style? style)
+        {
+            if (calendar is null)
+            {
+                throw new ArgumentNullException(nameof(calendar));
+            }
+
+            calendar.HeaderStyle = style ?? Style.Plain;
+            return calendar;
+        }
     }
 }