    The 'phong' keyword controls the amount of Phong highlighting on the
 object.  It causes bright shiny spots on the object that are the color of
 the light source being reflected.

    The Phong method measures the average of the facets facing in the mirror
 direction from the light sources to the viewer.

    Phong's value is typically from 0.0 to 1.0, where 1.0 causes complete
 saturation to the light source's color at the brightest area (center) of the
 highlight.  The default phong 0.0 gives no highlight.

    The size of the highlight spot is defined by the phong_size value.  The
 larger the phong_size, the tighter or smaller, the highlight and the shinier
 the appearance.  The smaller the phong_size, the looser, or larger, the
 highlight and the less glossy the appearance.

    Typical values range from 1.0 (Very Dull) to 250 (Highly Polished) though
 any values may be used.  Default phong_size is 40 (plastic) if phong_size is
 not specified.  For example:
       finish {
          phong 0.9
          phong_size 60
       }

    If 'phong' is not specified then 'phong_size' has no effect.
