Got it to build.

include/list.h

@@ -28,10 +28,41 @@ list_t *list_new(size_t memb_size, size_t capacity);
 void list_free(list_t *list);
 
 /*
- * Adds an element to the end of the list.
+ * Frees a list, calling a function on each element before doing so.
+ * If list is null, no action is taken.
+ * DO NOT pass free as the callback. Use list_elem_free if
+ * you want to do that.
+ */
+void list_free_with(list_t *list, void callback(void *item));
+
+/*
+ * This is a convinience function designed to be used with
+ * list_free_with or list_foreach.
+ * It calls the stdlib free function on each element.
+ * We can't pass in free directly, as each pointer needs to be
+ * dereferenced first.
+ * This should only be used on lists of pointers that were
+ * allocated using malloc (or similar).
+ */
+void list_elem_free(void *item);
+
+/*
+ * Adds an element at the end of the list.
  */
 void list_add(list_t *list, const void *data);
 
+/*
+ * Adds an uninitialized element at the end of the list,
+ * and returns a pointer to it.
+ */
+void *list_alloc(list_t *list);
+
+/*
+ * Deletes the last element of the list.
+ * If the list is empty, no action is taken.
+ */
+void list_remove(list_t *list);
+
 /*
  * Adds an element at an arbitrary position in the list, moving
  * the elements past index to make space.