Add compatibility for collections.

[alex-w-k]

Collections are an attribute that can be returned from movies. It would be really nice to get collections the same way other tags are.

For example, movie.collections would return:

<Collection id="78376" filter="collection=78376" tag="Captain America"/>

in an array, as a collection class.

[jasmeralia]

I just came across this project today and my goal is to automate adding videos to different collections based off of the title. Using your PR, I am able to see collections on sections and videos inside a given section, but I'm not quite sure how to add a collection to a video. This repo links to some additional documentation, but that link seems to be broken at this point. Any advice would be appreciated.