Add visual examples of extrusion

git-svn-id: http://svn.osgeo.org/postgis/trunk@12769 b70326c6-7e19-0410-871a-916f4a2858ee
forgot to commit changes

git-svn-id: http://svn.osgeo.org/postgis/trunk@12770 b70326c6-7e19-0410-871a-916f4a2858ee
resize images and put a not about how the 3D was rendered.

git-svn-id: http://svn.osgeo.org/postgis/trunk@12771 b70326c6-7e19-0410-871a-916f4a2858ee