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
build/*
docs/*
.sconsign.dblite
.sconf_temp
.optioncache
config.log
tools/cpuflags