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/calcurse.c

@@ -333,7 +333,7 @@ static inline void key_generic_reload(void)
 	todo_init_list();
 
 	io_load_todo();
-	io_load_app();
+	io_load_app(NULL);
 	io_unset_modified();
 	ui_todo_load_items();
 	ui_todo_sel_reset();
@@ -684,7 +684,7 @@ int main(int argc, char **argv)
 	wins_erase_status_bar();
 	io_load_keys(conf.pager);
 	io_load_todo();
-	io_load_app();
+	io_load_app(NULL);
 	io_unset_modified();
 	wins_slctd_set(conf.default_panel);
 	wins_resize();