Resolve "Add clone function"

Closes #11 (closed)

stack.c

@@ -16,3 +16,12 @@ void stack_peek(stack s, int *value){
         *value = s.data[s.top];
     }
 }
+
+void stack_clone(stack s, stack *clone) {
+    clone->top = s.top;
+    clone->capacity = s.capacity;
+    clone->data = malloc(sizeof(int) * s.capacity);
+    for (int i = 0; i <= s.top && i < s.capacity; i++) {
+        clone->data[i] = s.data[i];
+    }
+}
\ No newline at end of file