Add video file as enclosure in RSS feed item

[Art4]

Hi,

this PR sets the video url as an attached media object to the RSS feed item. This should fix #75.

Possible enhancements to this PR would be the mime type of the video, but I wasn't sure how to get this data from the elaticsearch result.

            enclosure: {
              url: item.url_video_hd || item.url_video,
              type: '', // mime type?
              size: item.size
            }

Also see the RSS spec as reference: http://www.rssboard.org/rss-specification#ltenclosuregtSubelementOfLtitemgt

[bagbag]

looks good

[bagbag]

Thanks!

The rss package MVW uses automatically determines the mime type based on the filename in the url.