[Discussion] #include method on base collection

Throwing this out there for discussion...  I'm going to need to make *a lot* of API calls to get the view_counts and such of videos, and I'd like a way to do that as efficiently as possible (both time and quota).

Each call to the API is one additional quota unit, as well as ~300ms waiting.  Through `yt` there is no way to do this in bulk yet.

This PR would allow me to get the statistics of batched videos.

What do you think about adding an `include` method to specify additional parts?

```ruby
Yt::Collections::Videos.new.include(:statistics, :content_owner_details).where(id: 'K9XCKP9KN7A').first
```