Give "iv" some love

by Ismael C for OpenImageIO

Iv, the image viewer included with oiio, currently only works with OpenGL 2.0 or superior and lacks some fancy and interesting tools which could be done with OpenGL, my proposal is to implement both. I also propose some "extended" objectives which are meant to be taken as optional and which not necessarily fall in the iv/OpenGL realm (but are cool, interesting and challenging anyway).