Forgot to commit the DirectionalLight.java file!!
Many modifications:

+ Implemented JitteredPointLight (Book: Exercise 18.1)
+ Implemented Ambient Occlusion (Book: 17)
+ Implemented the Buffer class to abstract image drawing; abstract the
WritableRaster layer which only has a max color-depth of 8 bits
(unsatisfactory!)
+ Introduced many new Constants (Samples, Width, Height, Zoom, etc)
    which allow easy parameter-changes in the future.