particle/list: optionally destroy sub particles

This was always done before. Now that it is optional, one can for
example generate lists dynamically, using the same set of base
particles over and over again.

config.c

@@ -166,7 +166,8 @@ particle_list_from_config(const struct yml_node *node,
     }
 
     struct particle *list = particle_list_new(
-        parts, count, left_spacing, right_spacing, left_margin, right_margin);
+        parts, count, left_spacing, right_spacing, left_margin, right_margin,
+        true);
 
     free(parts);
     return list;