Not a particularly exciting release:

• Linux: Fix compilation bug with Ruby 2.0
• Mac: Use full Retina resolution where available
• All: Add Image#subimage(x,y,w,h) / ImageData::subimage(x,y,w,h)

I'm not sure if the last method has many use cases, but it makes it possible to cleanly load texture atlases from Gosu (if anyone writes a method to do so). This is not generally necessary, but I'd like to toy around with this some time.

For Retina support, it would certainly be great to have support for @2x images in Gosu, but I'm not sure how this would/should work. I'm open to suggestions :)

I'll update the app wrapper & docs later.