Use generic lists for todo items.

Use the new generic list implementation instead of "next" pointers in
todo items.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.c

@@ -77,6 +77,7 @@ main (int argc, char **argv)
 
   /* Initialize non-thread-safe data structures. */
   event_llist_init ();
+  todo_init_list ();
 
   /*
    * Begin by parsing and handling command line arguments.