Added render subdirectory
Formatted doxygen comments
Added API independent rendering classes
Geometry class is used to represent 3d models
GlobalState classes are used to represent render states
Base class for the nodes in the scene graph
Node that represents a render state for its children
Base class for api implementation
Class containing information on the window on which we will render
Interface to use rendering functions
Scene graph to use to render
Spatial node used to represent node's transformations
Added test units for rendering classes