spritezero-like library for .png image resources.
spritezero library requires .svg image resources for retina support.
But retina support is also possible with two sets of .png images(small and large).
for whom doesn't have .svg or who are not able to generate .svg, it would be a good alternative.
Prepare two sets of images for sprite and sprite@2x which has the same list of files.
spritezeropng -o <out_folder> <path_for_sprite> <path_for_sprite@2x>