flesh out png support in shell script
flesh out png support in shell script

jibsen/imgmin,rflynn/imgmin,micmro/imgmin,rflynn/imgmin,pornel/imgmin,pornel/imgmin,pornel/imgmin,rflynn/imgmin,micmro/imgmin,micmro/imgmin,micmro/imgmin,rflynn/imgmin,jibsen/imgmin,jibsen/imgmin,pornel/imgmin,jibsen/imgmin