File Processor #116

hey @sergcen im interested in implementing a file-processor, to e.g. minify/optimize the to be processed image.

something like like this:

{
            url: "copy",
            assetsPath: "somepath",
            shrink: 8,
            fileProcessor: (content, file) => {
                return imagemin.buffer(content, {})
            }
}

as it is an async process i guess this module needs some massive async refactoring (im seeing an open PR, maybe this can be a starting point)

or do you have some other idea simpler idea for chaining in some image optimizations?!

are you interested in a PR?