Address issue with comment handling in the splitter

This pull request will fix an issue that destroys CSS files that contain protocol independent urls (for example: `background-image: url(//assets.myserver.com/asset.png)`).

It also addresses the issue of wrongfully parsed multiline comments.

Not that this changes the current behavior as it will no longer remove `//` comments. This should be the correct behavior since `//` is not a valid CSS comment.