fixed several 'retina display' images and added a bunch more (though just from upscaling the normal ones; might be nice to have 'em redrawn at a real higher resolution)
foreach(dir
Art
Bamboo
Bath
Blox
Brick
Cake
Castle
Cheese
Christmas
Compost
Deepspace
Desert
City
CrazyMission
EarthRise
Eyes
Freeway
Golf
Halloween
Hell
Island
Jungle
Nature
Olympics
Planes
Sheep
Snow
Stage
Underwater
)
add_subdirectory(${dir})
endforeach(dir)