Merge: Brainfuck

As the name implies, this is a very simple Brainfuck interpreter written in Nit.

Yes, it is (mostly) useless, but it might serve as an example of a simple Nit program.

Pull-Request: #828
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>