Merge: More Rosetta Code

Because it is and easy task.

note that `tree_traversal` is not as nice as it could be. Maybe a visitor (or generator) should be used instead.
Moreover, a lot of code could be removed if #1274 is solved.

Pull-Request: #1337
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>