MEM_OVERFLOW_CHECK macro

MEM_OVERFLOW_CHECK: mem overflow protection reserves a configurable amount of bytes before and after each heap allocation chunk and fills it with a prominent default value. MEM_OVERFLOW_CHECK == 0 no checking MEM_OVERFLOW_CHECK == 1 checks each element when it is freed MEM_OVERFLOW_CHECK >= 2 checks all heap elements every time mem_malloc() or mem_free() is called (useful but slow!)