- allow youtube urls to start with `www`
- use `strings.Builder` instead of a `bytes.Buffer`
- use a `strings.NewReader` instead of a `bytes.NewBufferString`
- sprinkles a couple of `continue` to make the code-flow more obvious
- inline calls to `inList`, and put their parameters in the right order
- simplify isPixelTracker
- simplify `isValidIframeSource`, by extracting the hostname and comparing it
directly, instead of using the full url and checking if it starts with
multiple variations of the same one (`//`, `http:`, `https://` multiplied by
``/`www.`)
- add a benchmark
