Minify CSS URLs

[surrim]

minifyURLs doesn't pay attention to the following snippet:

<style>
    html {
        background-image: url("http://example.com/images/background-1.jpg");
    }
</style>

That's because html-minifier calls clean-css for inline CSS and clean-css doesn't use relateurl.
A possible solution for that would be to replace the url(...)-parts with html-minifier directly.

[alexlamsl]

clean-css has its own mechanisms for URL rewrites, namely rebase, relativeTo and root.

[alexlamsl]

In theory we can populate those fields I mentioned within minifyCSS when they are not specified by the user, and minifyURLs.site is defined.

@kangax @XhmikosR how do you feel about this?

[surrim]

Thanks for the cute patch, works fine here.

[alexlamsl]

Thanks for testing. 👍