Add support for CSS Modules global class composition & compose-with

[mmrko]

As of postcss-modules-extract-imports@1.0.0 and postcss-modules-scope@1.0.0 CSS Modules supports global class composition and the compose-with keyword:

css-modules/postcss-modules-extract-imports#9
css-modules/postcss-modules-scope#20
css-modules/postcss-modules-scope#21