Implement basic light sampling. Very noisy.
Shut-up CRT deprecation warnings.
Fix bug in orient() when vectors aren't perpendicular
Add sqr and length_sqr functions
Add funcs to convert from/to XYZ and xyY colorspaces
Remove duplicated call to std::cos
Add vmax/vmin function that return by value.

For details see: http://randomascii.wordpress.com/2013/11/24/stdmin-causing-three-times-slowdown-on-vc/
Optimize sphere sampling code using trig identity