Rebuilt js

Completely rebuilt code to move config from html to a js object.

Added ability to lazy-load images.
JS Linted code
V2 complete

Updated the README to take account of the new ways of working.

Removed the old code and updated the demo.html.

Fixed a bug with lazy-loading not updating on page resize sometimes.

Allowed classes to be passed to the image.

Allowed noscript option and new responsive-image tag.
Added minified js
Merge pull request #1 from dittto/v2

V2