This header file is a library for writing images to C stdio or a callback.
The PNG output is not optimal; it is 20-50% larger than the file written by a
decent optimizing implementation; though providing a custom zlib compress
function (see STBIW_ZLIB_COMPRESS) can mitigate that. This library is designed
for source code compactness and simplicity, not optimal image file size or
run-time performance.
