rename Python module from 'raytracer' to 'pyrit' improve Python binding: - new objects: Container, Octree, KdTree, Shape, Pixmap, Sampler, DefaultSampler - all shapes are now subclasses of Shape - clean, remove redundant Getattr's - Raytracer render method now just wraps C++ method without doing any additional work adjust all demos for changes in Python binding, remove PIL dependency add demo_PIL.py as a example of pyrit + PIL usage render_nff.py now either loads file given as a argument or reads input from stdin otherwise fix bug in pixmap float to char conversion

use SSE for float to char image buffer conversion

merge pixmap handling from sampler, material.h and ccdemos's image module to new Pixmap class add check for PNG library, allow writing PNG file from a Pixmap simplify demos using new methods from Sampler and Pixmap