Fixing ListFun.addEle with position

[joaoemilioml]

First, the add is 1 indexed instead of 0 indexed like other structures would be (and as the remove is)

This test case for example:

ListFun<Integer> list1 = ListFun.list(3, 6, 9, 8);
list1.addEle(3, 25).forEach(System.out::println);

Will give: 3, 3, 25, 6, 9, 8 (the head is repeated twice).

This will happen for any index greater than 2.

Also, this part:

if(pos == 0)
   return this.tail().addEle(ele);

Would replace the object at the given position with the new value instead of adding it and keeping the other elements of the list.