added gradient reference images
mse and psnr working for rasterific
add cairo support
GHC to 7.8.3
regenerate reference images with cairo (except for gradients)
merge master
Merge branch 'master' into pixel
Update README.md
postscript support
add alpha layer to postscript and wrap svg in figure
adjust postscript, something wrong? mse to high
svg
adjust image magick for RGBA8
svg handle transparency
make eps transparent
Merge pull request #3 from diagrams/pixel

I'm going to merge this branch even though postscript needs some work.
Everything else is working and it will hopefully be useful as we want to test after merging `generalized-double`