Feature/oembed support

Hi @remy!

This is a first attempt to implement oEmbed support for JSBin. oEmbed allows you to embed rich content without running arbitrary code (unlike the current embed method) and therefore is the prefer method for a lot of people including Gitter, here some more info: http://oembed.com/ and some examples: https://embed.spotify.com/oembed/?url=http://open.spotify.com/track/4fyHcNgv4PizcRMXUGPFQ2

Here's how they would look:
![](http://i.imgur.com/lEmgNqc.png)

What do you think?
The config is actually loaded on to `app.settings`, and since `app` is available on every request object, you don't need the require. So the coe is just `.match(req.app.settings.url.host)` and one less require (which actually *does* count towards boot time!)