Implement the <img> srcset feature

[ryanholder]

srcset for some more information read - https://www.webkit.org/blog/2910/improved-support-for-high-resolution-displays-with-the-srcset-image-attribute/

I have an implementation of srcset in place however it does not currently have the ability to create more than 1 extra image size. It needs to be extended to work with more than 1 extra image size

[remkus]

Related: http://mobile.smashingmagazine.com/2013/08/21/webkit-implements-srcset-and-why-its-a-good-thing/

[ryanholder]

We are going to push this to version 1.1.0 and we will handle images in areas like the slider using WPThumb (more information on this in issue #121)

[remkus]

We can indeed start implementing this for 1.1.0 with Picturefill as a fall back

[ryanholder]

I would leave it for next release as we had agreed. It would make a nice item to add to a new release which could follow soon after the 1.0.0 version

[remkus]

Sorry, had already updated my comment. I meant 1.1.0 :)