Initial feedback for std.experimental.image

[Rikki Cattermole via Digitalmars-d]

Bumpity bump.
Updated.

Includes most of the PNG implementation for loading of images.
http://cattermole.co.nz/phobosImage/docs/html/std_experimental_image_fileformats_png.html
I've also added a little bit more to the specification document.

Next stream I'll be tackling IDAT chunk loading (not something I 
exactly enjoy).