calendarspec: allow repetition values with ranges

"Every other hour from 9 until 5" can be written as
`9..17/2:00` instead of `9,11,13,15,17:00`

src/basic/calendarspec.h

@@ -29,6 +29,7 @@
 
 typedef struct CalendarComponent {
         int value;
+        int range_end;
         int repeat;
 
         struct CalendarComponent *next;