moved position to the object class, updated the sphere constructor
added a normal function that will take a vector and returns a normalized copy of it
The scene class will be just a fancy data container for scene objects, lights, the camera, and the image plane
The object for the hit class is optional. Currently depends on boost::optional but will switch to std::optional once I get a c++14 compiler. Optional is typedefed in the common.hpp header for easyrefactoring later
new image plane class. simple class that just contains the image width, height and stores the aspect ratio.