use inheritance for ObjParser
use std::istream for Parse parameter
removed operator>> for obj
added group callback for obj
added group data to ObjBuffer
addeg face group to mesh io
added face group APIs to mesh
added shading group id to Intersection
set default group shader id zero
added face group name to mesh
removed iff_test
added geo_io.h
added member functions to MeshOutput
use MeshOutput member functions for obj2mesh
use MeshOutput member functions for velgen
made MeshOutput members private
made ShaderProgram members private
made ImageCard members private
renamed draw_image to image_card
renamed glsl_shaders to shader_program