Add CImg, C++ Template Image Processing Toolkit about single_file_libs

[jnareb]

Or even simpler example (from http://cimg.eu/CImg_slides.pdf):

#include "CImg.h"
using namespace img_library;
int main(int argc, char **argv) {
    CImg<unsigned char> img(300,200,1,3);
    img.fill(32);
    img.noise(128);
    img.blur(2,0,0);

    const unsigned char white[] = { 255,255,255 };
    img.draw_text("Hello World",80,80,white,0,32);
    img.display();

    return 0;
}

[nothings]

I think 60KLoC is kind of borderline, but I won't reject it for that reason.

It's a little unclear to me what someone is supposed to actually do to choose between the licenses when incorporating the project into their source tree. I wish the author would clarify that, but I'm not going to reject listing it just for that.

So... added!