Created by: semenko
More thoroughly compress PNGs using optipng and pngcrush.
(h/t to Chromium for their compression strategy, e.g. https://chromiumcodereview.appspot.com/10426009 )
You can aggressively compress directory via:
find . -type f -name "*.png" -print0 | xargs -0 optipng -o7
find . -type f -name "*.png" -print0 | xargs -0 pngcrush -reduce -brute -rem iTXt -rem tEXt -rem zTXt -rem tIME -ow