Links between classes in documentation app

It would be extremely helpful if wherever other classes are referenced, the documentation linked to that class. Currently, you generally have to go back to some route point and find each class yourself.

For example (from Router):

```
currentInstruction: NavigationInstruction

The currently active navigation instruction.
```

NavigationInstruction should link to the navigation instruction class definition.

Start with the Router documentation example and inspect how the NavigationInstruction class definition is represented. Trace how class references are rendered in the documentation app, then verify that referenced classes link to their definitions wherever they appear.

Written by the indexing model from the issue text.