fix a format string issue in array test ARRAYLIST_IDX deals with the head pointer. Explicitly cast to unsigned long and use %lu in the format string. Clang 10.0.1 used to complain as follows: arraylist_test.c:19:2: warning: format specifies type 'int' but the argument has type 'long' [-Wformat] arraylist_test.c:15:24: note: expanded from macro 'dump' printf("[%d] %d\n", ARRAYLIST_IDX(p, list), *p); \ ~~ ^~~~~~~~~~~~~~~~~~~~~~

add arraylist_test