Run pngquant on subfolder

This runs pngquant on all png files in the current directory and subdirectory and optimized them in place.

fish:

for file in (find . -name '*.png')
    pngquant --verbose --speed 1 --force --ext '.png' $file
end

shell:

for file in `find . -name '*.png'`; do
    pngquant --verbose --speed 1 --force --ext '.png' $file
done