Generalized the single icon export.
Retina and/or Standard images can be exported in a single step.
Square scaling 1 for 1 width and height.
Rectangular scaling that preserves the original image's proportions.
Cleaner interface.
Saving png background and gamma attributes.
Using gimp-image-merge-visible-layers to combine layers instead of gimp-image-flatten.
Updated documenation.
Removed .gitignore