Create a /person/known_for method

Doubtful I'll ever push a dedicated method for this. Now that we have the 'combined_credits' method, this is really easy to generate yourself.

All we're doing on TMDb is taking the /combined_credits method, uniquing the movie and TV fields by id and then joining them. Next, sort by vote_count and grab the first X that you're interested in.

Cheers.

For anyone finding this ticket after the fact, this is now possible to generate client side since all of the person credit methods are returning the standard media objects now. For more information see: https://developers.themoviedb.org/3/people/get-person-combined-credits

I'm re-opening this, now that the website has a real calculated known for field, I'll bring this field (and maybe results) to the API. No ETA.

One more update... The person method now includes a known_for_department which you can use to know what department to build a persons "known for" data with.