Add item filters

This adds the following filter options that allow for restricting the
set of items that are read from the appointments file:

* --filter-type
* --filter-start-from
* --filter-start-to
* --filter-start-after
* --filter-start-before
* --filter-end-from
* --filter-end-to
* --filter-end-after
* --filter-end-before

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

src/dmon.c

@@ -165,7 +165,7 @@ void dmon_start(int parent_exit_status)
 	event_llist_init();
 	recur_event_llist_init();
 	todo_init_list();
-	io_load_app();
+	io_load_app(NULL);
 	data_loaded = 1;
 
 	DMON_LOG(_("started at %s\n"), nowstr());