feat: add Zillow module

[shredzwho]

This PR adds a new shopping module for Zillow.

[kaifcodec]

@shredzwho We don't need a separate test file for each module, so you can remove it.

One thing we've recently introduced is the extra parameter in Result.taken() to pass any additional data that a site exposes about a user. If this site returns profile metadata publicly, try extracting those details with regex (or another appropriate parser) and pass them through extra.

If the profile data is only available after login or signup, let me know and I will merge it as it is for now.