The missing part of the Elm guide: URL handling with Browser.application

I saw a tweet from someone who was confused by the missing section in the URL Parsing chapter of the Elm 0.19 guide.

The chapter shows several examples of URL parsers made with Url.Parser, but the Synthesis section at the end is just a TODO. However, the section does suggest what should be in it:

> The major new things are:
> 1. Our update parses the URL when it gets a UrlChanged message.
> 2. Our view function shows different content for different addresses!
>
> It is really not too fancy. N...