Update RB Tree:
Update RB Tree:

* Fix issue of the searched element is the root node (See #93)
for _it_from. It now returns a proper iterator.

* Update _it_from to match the last documentation:
if there is no element lower or equal to the searched node,
it returns a null iterator.

* Update _it_while_p so that it returns false if it is null iterator.

P-p-H-d/mlib,P-p-H-d/mlib