Added return value for the node_init

- Can be used as before, but cleaner interface in parser.y

exercises/02/vslc/include/ir.h

@@ -16,8 +16,10 @@ typedef struct n {
  * @param *data associated data. Declared void to allow any type
  * @param n_children number of children
  * @param ... variable argument list of child nodes (node_t *)
+ * 
+ * @return Pointer to the initialized node
  * */
-void node_init (
+node_t* node_init (
     node_t *nd, node_index_t type, void *data, uint64_t n_children, ...
 );
 #endif