Add supplementary views

[Steven4294]

Hi, I'm using this library for a social media app to display photos. It would be nice to be able to add a view to the photo to show comments, likes, etc...

[njdehoog]

Hi Steven, I think adding support for supplementary views is a good idea. For me this is currently not a priority to work on, but feel free to take a shot at it and issue a pull request.