Rename user customizable macros

to be compliant with other
and clearer that they can be customized.

tests/test-mdeque.c

@@ -52,7 +52,7 @@ static void test_ti1(int n)
   deque_t d;
 
   deque_init(d);
-  assert(deque_capacity(d) == M_D3QU3_DEFAULT_SIZE);
+  assert(deque_capacity(d) == M_USE_DEQUE_DEFAULT_SIZE);
   
   for(int i =0; i < n ;i++) {
     deque_push_back(d, i);