Add webmention support

![](http://dissociatedpress.com/wp-content/uploads/2011/02/oh-the-huge-manatee.jpg)
This is often referred to as the Law of Demeter. There are a few ways to handle this. I would probably do something like this for each of the author_* methods:

```ruby
def author_name
  name = entry.author_name
  name ||= card.try(:name) # I hate this, but meh, it's okay
  name ||= URI.parse(source).host
end
```

And then create an `author_name` on entry.
```ruby
def author_name
  try(:author).try(:format).try(:name) # ugh, there's probably a further way to improve this, more than I can say in these comments
end
```