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

Sphere, Box - RayPacket intersection replace 5x oversampling with 4x uniform oversampling

BBox - RayPacket intersection clean up

implement triangle packet intersection

prepare kd-tree traversal for packet tracing (4 rays at once) RayPacket and VectorPacket structures for packet tracing remove some redundant const's

vectorize makeRayPacket() using SSE intrinsics

prepare structures for packet tracing (it's already slightly faster, even without any explicit parallelization) supply missing virtual destructors

add 2D pixmap texture class

remove forgotten noise.h includes common_ply.h: ignore invalid faces with duplicated points (this solves visual flaws in dragon model) extend loadShape for loading triangles realtime_dragon.cc demo: add kd-tree dump/load functionality, add colored perlin cloud texture

material and texture classes moved to material.(cc,h) 2D texture mappings from textures.cc polished and moved to material.h add ColourMap class and subclasses to make textures more flexible two example textures: CheckersTexture and CloudTexture (using Perlin noise)

move shapes to extra source file add serialize header and source file with common serialization functions dump/load feature for shapes and kd-tree fix few minor bugs

rewrite subsampling from old code to DefaultSampler render in phases, clean workers after each phase

kd-tree: move recursive build subroutine from KdNode to KdTree

unify capitalization of method names in C++ and Python

kd-tree traversal - avoid dynamic memory allocation use minimum storage size for KdNode (8B on 32bit cpu) vector.h - add division operator, fix semicolons