new make infrastructure generalize floats to Floats, allow compiling as both double/float

naive color driven sub-sampling slightly optimized KdTree::nearest_intersection fixed bug in Box::intersect fixed stripes on spheres in spheres_ao.py (was caused by AO distance) new KdTree property: max_depth minor changes in realtime.py

new C++ demo: realtime.cc (real-time scene viewer using SDL) Quaternion, Camera::rotate and Camera::move replace all printf's with infomsg wrapper don't allocate memory in Raytracer::render, just blindly write to provided address don't creat Container object in Raytracer, let user do it