History for CMGUI lights and materials

changed:
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This tutorial draws content from some examples, particularly example a2 and example a/per_pixel_lighting

This tutorial is intended to get you to understand the different ways lighting and materials can be made to make you
scenes look better in cmgui.

1. **Default lights**.  In CMGUI the default lighting is a directional light that is attached to your view, you can 
   consider it a sort of headlamp.  This default light is slightly above you and pointing slightly down.
   Here I have loaded up a slightly deformed cube and drawn surfaces on it.

   <img src="default_light.png" />

   This is the script that generates this image, default_light.com::

     gfx read elements bicubic_linear_cube.exelem;
     gfx create win 1;
     gfx modify window 1 view parallel eye_point -1.30343 -2.5881 1.50531 interest_point 0.505811 0.497157 0.48454 up_vector 0.144703 0.233287 0.961581 view_angle 40 near_clipping_plane 0.0371942 far_clipping_plane 13.2919 relative_viewport ndc_placement -1 1 2 2 viewport_coordinates 0 0 1 1;
     gfx modify window 1 set perturb_lines;
     
     gfx modify g_element single surfaces select_on material copper selected_material default_selected render_shaded;

   You can list the parameters of this light like this::

     gfx list light default;

   Which in this case returns::

     light : default : infinite
       colour  red = 1, green = 1, blue = 1
       direction  x = 0, y = -0.5, z = -1