TODO: updates following Samuel's comments

TODO

@@ -8,18 +8,18 @@ TODO list
 
 - Make struct starpu_buffer_descr private (or not, as it can still be used in tests and examples)
 
+- Set task->buffers to NULL
+
 - Update all tests and examples
 
 - Depreciate cost_model field in struct starpu_per_arch_perfmodel
                                  struct starpu_perfmodel
 
-- Add a field cost_model_new
-  double (*cost_model_new)(starpu_data_handle_t *); /* returns expected duration in µs */
+- Add a field cost_function
+  double (*cost_function)(starpu_data_handle_t *, enum starpu_perf_archtype arch, unsigned nimpl); /* returns expected duration in µs */
 
 - Update all cost functions in examples
 
-- Set task->buffers to NULL
-
-- When cost_model is provided, but not cost_model_new, need to rebuild a struct starpu_buffer_descr
+- When cost_model is provided, but not cost_function, need to rebuild a struct starpu_buffer_descr
 
 - Update doc and changelog