Better support for Holder.js

[kidwm]

http://imsky.github.io/holder/

Holder.js is a client-side and retina-ready placeholder image tool.

[mistergraphx]

Why don't use www.lorempixum.com as an external images placeholder service ? Fixie approximately do the same job than holder.js if you specify a width and height exept the ability to choose the color maybe ...