[enhance] Set: choose become quicker
It gave the minimum element in O(log(n))
Now it works in O(1), giving the element in the top of the tree
[feature] libbase: Taking an element to show the difference between …
Usefull to explain why two sets are not equal.
[feature] libbase: choose_opt in Maps and Sets
Same as choose, but giving an option instead of an exception on empty map/set
Initial open-source release