at2x retina image function - fix bug 898013

rename at2x to hires as per jpetto's recommendation

fix bad search/replace

Use the media helper function to append URLs

Initial work on some image documentation

Switch to a suffixed hi-res image

change the second parameter of hires_img()
to be a simple dictionary  This allows naming the keys however we want instead of having to name them as valid python vars. Useful when the attribute has a dash in it. platform_img() has the same change in PR 1170

at2x retina image function - fix bug 898013

rename at2x to hires as per jpetto's recommendation

fix bad search/replace

Use the media helper function to append URLs

bring docs up to date