Removed Sphere struct.

It's simpler to just provide the parameters directly in the function.
Added TransformPair
Added matrix transform operator to Ray.
Fixed broken operator= in Optional
solve_quadratic always returns smallest root in x1
Added Ray evaluation operator.
Clamp colors before converting to sRGB to prevent artifacts.
Fixed handedness of orient function.
Moved sRGB encoding function to separate file.
Moved misplaced file from libyuriks
Invert order that transformations are written.

This should feel more natural. Transforms are chained in sequence
instead of in reverse.
Added sRGB -> linear mapping function.
Added SortedVector
Added several misc. libraries.
More imports and several C++11 cleanups.
Rename a confusing variable name.
Merge commit 'e46a2b3bd6afa0df48250e92265bbee1bd6bc2d2'
Implement basic light sampling. Very noisy.
Timestamp output image filenames.