Merge: Extends chars, string and stream with some whitespace-related function

While thinking about the remaining task of #466 (simple parsing), I though that there useful functions where missing in order to have a sane `Reader::read_word` method

Pull-Request: #1179
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc lib/standard/kernel.nit
Simple merge

diff --cc tests/sav/nituml_args3.res
Simple merge

diff --cc tests/sav/nituml_args4.res
Simple merge