feat(hmp): allow the user to specify a callback for dealing with their alloced mem

ds.c

@@ -153,7 +153,7 @@ ds_hmp_t
 }
 
 void
-ds_hmp_free(ds_hmp_t **hmp)
+ds_hmp_free(ds_hmp_t **hmp, void kv_callback(_ds_hmp_kv_t *kv))
 {
 	int i;
 	_ds_hmp_kv_t *kv;
@@ -167,6 +167,9 @@ ds_hmp_free(ds_hmp_t **hmp)
 		ll = (*hmp)->data[i];
 		while (ll && ll->data) {
 			if ((kv = ds_sll_remove(&ll, 0))) {
+				if (kv_callback) {
+					kv_callback(kv);
+				}
 				free(kv);
 			}
 		}