Added conversion from awt Polygon to scrimage Polygon
new colorModels and rasters
Merge branch 'master' of https://github.com/gwenzek/scrimage
Merge branch 'master' of https://github.com/sksamuel/scrimage
better factory for raster
removed channel size (always 1)
added png reader that directly fill the Raster
moved PNGMymeTypeChecker inside PNGReader
added documentation for Raster and ColorModel