To Webp Function

A simple for loop to make using globs easier with cwebp.

function towebp -d "Convert image files to web with cweb"

    for SOURCE_IMAGE in $argv
        set OUTPUT (path change-extension webp $SOURCE_IMAGE)
        cwebp $SOURCE_IMAGE -o $OUTPUT
    end
end

I'm pretty sure I saw a one-liner to do this (using pipes) but it was hard to understand so I thought this would make it clearer to myself what is going on, rather than just copying a command I can't figure out.