Implemented step for unfold and partial fold
Implemented depth limiting function for Trees
Replaced litTrace with hylomorphic solution

Lighting calculations logically separated from construction of
ray tree.  This will allow for alternate reflection sampling algorithms
to be substituted, such as Kajiya's method.
Merge branch 'rayTree' (early part) into next

Conflicts:
	Light.hs
Tweaked reflection and diffuse properties

Hopefully to prevent objects from emitting more light than
was incident.
Updated twoLights.ppm