basic support for css modules via <style module>

[akanix42]

This adds support for CSS modules following the implementation used by vue-loader.
To use CSS modules, you add the module attribute to your style tag:

<style module>
.test {
  color: red;
}
</style>

Then you reference it via the $style computed property:

<div :class="$style.test">Hello!</div>

I also fixed a typo on the postcss call ("form" -> "from") since I needed the full path... and then I of course had a typo in that commit message. 😊

This does not include support for composing from other CSS modules files, since to do that we have to call back to the compiler and either pull the file from cache or compile it on the fly and return the result. We would also have to pull in other file types on demand and process them (composing from say a .scss file).
Composing from global works, of course, since that doesn't require us to load those files.

[Akryum]

Thanks for your contribution! 😄