Lazy load images and Picturefill
Loads images when element is in view.
picturefill usage: https://github.com/scottjehl/picturefill/blob/master/README.md
pinched ideas from:
Loads images when element is in view.
picturefill usage: https://github.com/scottjehl/picturefill/blob/master/README.md
pinched ideas from: