[Feature] add CSS Modules (`postcss-modules`) support

[michael-ciniawsky]

https://medium.com/@sokra/79583bd107d7
css-modules/css-modules#240
css-modules/css-modules#241

[felixsanz]

@michael-ciniawsky Looks like with 2.x my CSS modules are now broken. Is this related?

Is there a workaround? Thanks!

[michael-ciniawsky]

@felixsanz Are you using LoaderOptionsPlugin in your webpack.config.js? Normally it shouldn't affect the CSS Modules implementation of css-loader, but this was claimed a few times now. #232 #222

[TrySound]

Shouldn't postcss-modules use messages for output instead of callback for this feature?
Btw, this works great in modular-css

[felixsanz]

@michael-ciniawsky I'm using css-loader's modules: true option. I'm not using LoaderOptionsPlugin anywhere. I'll continue in #232