Merge: Rosettacode grayscale implementation

An implementation of Rosettacode's grayscale task (http://rosettacode.org/wiki/Grayscale_image) with additional features, including creating a Bitmap from scratch and manipulating its individual pixels.

Pull-Request: #1282
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>