2048x2048 png files are taking 10 seconds to save

[rainlizard]

I've solved the issue, and can make them save in 0.32 seconds. In save_image_extended.py, set these lines to:

png_compress_level = 0
optimize_image = False

This comment seems to be incorrect, since it is in fact affecting PNG: # optimize_image only works for jpeg, with like just 2% reduction in size

I'm not sure if making a pull request is appropriate because this is disabling compression which ideally should be optional I think.