Link to nested type

Related to #235, it would be nice if nested types would be linked to:

```swift
enum Namespace {
  struct A {}
}

/// - Returns a `Namespace.A`.
func example() -> Namespace.A { Namespace.A() }
```

Here, the generated HTML currently links the "Namespace" part in the code snippet for the `example()` method, but not the "A" part.