C Dynamic-Array, non generic (int) implementation

Copyleft 2017 by lion137

 Usage:    
 array_int * x = array_int_init(); // constructor    
 functions over structure, all O(1):    
 - append (add at the end);    
 - pop;    
 - size;    
 - is_empty;  
 - nth(obj, index) (peek the indexed element in the array);    
 - update(obj, elem, ind) (sets the ind - th elementh in the array to elem)    
 - print.      
 Delete object by call delete(obj) and set obj to NULL.