Links in markdown do not trigger onUrlRequest in Browser.application

Hi @evancz! Thanks for great work with 0.19 - community was waiting for this for a long time, you know.

However, I've got an unexpected behaviour of interaction between `Browser.application` and `Markdown`. The problem is Markdown's links don't work like external links in case when they are linked with internal routes (`"/"` for example). Furthermore clicks to the links don't trigger neither `onUrlRequest` nor `onUrlChange` - browser just load a page from scratch.

I guess it happens because the module insert links as is and without handling of click event.

I've made an [Ellie example](https://ellie-app.com/3bH5tffcHcRa1) but it won't work inside of the sandbox so you should run it locally thru `elm reactor`.