Add support for oembed service?

[pdehaan]

Was reading https://medium.com/slack-developer-blog/everything-you-ever-wanted-to-know-about-unfurling-but-were-afraid-to-ask-or-how-to-make-your-e64b4bb9254#.cchchs8s3 and started looking into http://oembed.com/.

Not sure if it's worth it to try and search for oembed service stuff in a webpage instead of trying to scrape a page's DOM and extract tags.

Here's 3 results from random tabs that I happened to have open:

1. https://www.youtube.com/watch?v=qjwujvv1E0w&feature=youtu.be:

   <link rel="alternate"
       type="application/json+oembed"
       href="http://www.youtube.com/oembedurl=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3Dqjwujvv1E0w&amp;format=json" 
       title="Urban Agriculture in Focus: Greenhouse vs. Indoor Growing">

   Output:

   {
       "author_name": "Bright Agrotech",
       "author_url": "https://www.youtube.com/user/BrightAgrotechLLC",
       "height": 270,
       "html": "<iframe width=\"480\" height=\"270\" src=\"https://www.youtube.com/embed/qjwujvv1E0w?feature=oembed\" frameborder=\"0\" allowfullscreen></iframe>",
       "provider_name": "YouTube",
       "provider_url": "https://www.youtube.com/",
       "thumbnail_height": 360,
       "thumbnail_url": "https://i.ytimg.com/vi/qjwujvv1E0w/hqdefault.jpg",
       "thumbnail_width": 480,
       "title": "Urban Agriculture in Focus: Greenhouse vs. Indoor Growing",
       "type": "video",
       "version": "1.0",
       "width": 480
   }

2. http://www.greenkitchenstories.com/the-green-kitchen-smoothies-book/:

   <link rel="alternate"
       type="application/json+oembed"
       href="http://www.greenkitchenstories.com/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fwww.greenkitchenstories.com%2Fthe-green-kitchen-smoothies-book%2F" />

   Output:

   {
     "author_name": "Green Kitchen Stories",
     "author_url": "http://www.greenkitchenstories.com/author/greenkit/",
     "height": 338,
     "html": "<iframe sandbox=\"allow-scripts\" security=\"restricted\" src=\"http://www.greenkitchenstories.com/the-green-kitchen-smoothies-book/embed/\" width=\"600\" height=\"338\" title=\"Embedded WordPress Post\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\" class=\"wp-embedded-content\"></iframe>",
     "provider_name": "Green Kitchen Stories",
     "provider_url": "http://www.greenkitchenstories.com",
     "title": "Green Kitchen Smoothies",
     "type": "rich",
     "version": "1.0",
     "width": 600
   }

3. https://www.flickr.com/photos/bees/2341623661/:

   <link rel="alternative"
       type="application/json+oembed"
       href="https://www.flickr.com/services/oembed?url&#x3D;https://www.flickr.com/photos/bees/2341623661&amp;format&#x3D;json" />

   Output:

   {
     "author_name": "‮‭‬bees‬",
     "author_url": "https://www.flickr.com/photos/bees/",
     "cache_age": 3600,
     "flickr_type": "photo",
     "height": "683",
     "html": "<a data-flickr-embed=\"true\" href=\"https://www.flickr.com/photos/bees/2341623661/\" title=\"ZB8T0193 by ‮‭‬bees‬, on Flickr\"><img src=\"https://farm4.staticflickr.com/3123/2341623661_7c99f48bbf_b.jpg\" width=\"1024\" height=\"683\" alt=\"ZB8T0193\"></a><script async src=\"https://embedr.flickr.com/assets/client-code.js\" charset=\"utf-8\"></script>",
     "license": "All Rights Reserved",
     "license_id": 0,
     "provider_name": "Flickr",
     "provider_url": "https://www.flickr.com/",
     "thumbnail_height": 150,
     "thumbnail_url": "https://farm4.staticflickr.com/3123/2341623661_7c99f48bbf_q.jpg",
     "thumbnail_width": 150,
     "title": "ZB8T0193",
     "type": "photo",
     "url": "https://farm4.staticflickr.com/3123/2341623661_7c99f48bbf_b.jpg",
     "version": "1.0",
     "web_page": "https://www.flickr.com/photos/bees/2341623661/",
     "web_page_short_url": "https://flic.kr/p/4yVr8K",
     "width": "1024"
   }