build script fixes, add ldflags build option
update and enhance demos
fix bug in 4x grid oversampling
warn if writePNG called while compiled without libpng
make shapes in ShapeList const
and add many other const needed due to snowball effect
slightly optimize Camera::makeRayPacket using _mm_shuffle_ps
make Vector SIMD vectorization disabled by default (causes problems)
fix bug in implicit reflection of transmissive surfaces,
when surface's reflection parameter is set to zero
Bugs
====
* Mingw + SSE does not work
Future Plans
============
* Python binding for material.h classes
* Container should implement Shape interface to allow building hierarchies
* Container should allow local space transformations
* generalization: Camera "shader" (ray generator), surface shader and maybe light & background shaders
* put everything into a namespace
* stochastic oversampling
* absorbtion of refracted rays in dense materials (can be computed using shape distance and some 'absorbance' constant)