Optimize raster graphics

Use a combination of [OptiPNG, PNGCrush, AdvPNG, PNGOUT,
Gifsicle](http://imageoptim.com/) to reduce image size by a total of
over 1.1MB.
Merge pull request #114 from oo12/bbf214a1592774ac75be11d22f15217a2ff15712

Optimize raster graphics (PNG and GIF)