Add support for building IO against stb_image.h from nothings/stb collection of single-file libraries

[mloskot]

There is collection of single-file libraries https://github.com/nothings/stb which includes stb_image.h offering image loading/decoding from file/memory: JPG, PNG, TGA, BMP, PSD, GIF, HDR, PIC.

An interesting dependency-less alternative that is simpler to build the GIL IO against.

[fsmoke]

I impatiently waiting implementation of this feature!!! Very, very need it!