smooth triangles (aka Phong shading)
extend Python binding to support vertex normals and smooth triangles
make bunny.py and realtime_dragon smooth, and fix other demos for new triangle constructor
add Vector::operator/=
tuned ray-triangle intersection, now there are three algorithms to choose from:
Plucker, Barycentric and Barycentric with preprocessing (Wald)
methods in Vector and Shape (and derivates) made const