Route component

This PR simplifies things quite a bit.

There are now only two types of React components: `Route` and `Link`. Both components are able to be rendered normally using `React.renderComponent`. Everything that was previously encapsulated in `Router` is now in `Route`, but only the top-level routes ever render. All others are used for configuration, as before.

The recommended usage is now:

```js
var routes = (
  <Route handler={App}>
    <Route name="user" path="user/:userId" handler={User}/>
  </Route>
);

React.renderComponent(routes, document.body);
```

which should be more familiar to React users than our custom `Router#renderComponent` method.

This work should help with #38 and #34.