media queries not included

hey,

your project inspired me, but my usecase is a bit out of scope, so I created my own package...

However, I found out, that `CSS.takeCoverageDelta()` doesn't include the media queries for a rule.
I tinkered a bit and outsourced the resulting parser in a separate package [coverage-delta-parser](https://github.com/paulpflug/coverage-delta-parser). Feel free to use or copy, it is rather small..

Start at the implementation of CSS.takeCoverageDelta() and trace how rules are parsed, then compare its handling with the coverage-delta-parser package linked in the issue. Done means media queries are included in the returned coverage delta and the behavior is covered by an appropriate test.

Written by the indexing model from the issue text.