Added tests

tests/02_calloc.c

@@ -0,0 +1,11 @@
+#define DEBUG
+#include <stdlib.h>
+#include "../include/mem.h"
+
+int main(void){
+    size_t nbytes = 20;
+    void *ptr = ALLOC(NOZERO, nbytes);
+    ASSERTED(ptr != NULL);
+    ASSERTED( !mem_is_zero(ptr, nbytes));
+    return EXIT_SUCCESS;
+}