Additional cleaning features

Right now CleanLink does the following:
- clean URLs by rewriting paths or removing query parameters
- detect embedded URIs and redirect or drop requests that contain them

I’ve just had to add another feature because Google was loading its URL redirect page in an iframe: we now “promote” the iframe request from `www.google.com/url?url=…` to the main frame in the tab. For now, this behaviour is hardcoded (see dbd58dc).

This could possibly be
- detected,
- generalized to more domains/iframe pages, and
- maintained in the rules.

Other features are not implemented as they have not been required until now, such as:
- matching query parameters on their value instead of (or additionally to) their key,
- rewriting query parameters
- any cleaning in the hash part of the URL (though we already detect embedded URLs in the hash if they start with `#!/`)

So please report in this issue any use cases for these or other link cleaning features and we’ll see about implementing them.

Start by reviewing commit dbd58dc and the existing URL-cleaning rules to understand the current iframe promotion behavior. The issue has no specific use case or entry point; it would need a defined cleaning behavior, affected domains or URL parts, and acceptance criteria before implementation is complete.

Written by the indexing model from the issue text.