Add support for retina icons

[Daniel15]

MacBook Pros have retina screens and use double density icons. Basically a 100x100 icon would be displayed in a 50x50 space on the screen.

To support with Stitches:

• Change default padding from 5px to 4px so it's always divisible by 2
• Add an option to output a Retina-friendly spritesheet:
  • Include background-size: x y to resize the image, where x is half the width and y is half the height of the image (eg. background-size: 250px 100px for a 500px by 200px spritesheet)
  • Halve all the background-position values

More information: http://miekd.com/articles/using-css-sprites-to-optimize-your-website-for-retina-displays/

[yarontt]

+1 to that. At least make sure the output .png's size is a multiple of two :)