Use HTML5 History API instead of hash

You could use [HTML5 History API](https://developer.mozilla.org/en-US/docs/Web/API/History_API) instead of `window.location.hash`. It allows to change state, title and URL of page without reloading the page.

One problem is that pages aren't real so refreshing the page will probably land on an invalid URL. Is it possible to handle that?

Here is a demo: https://html5demos.com/history/

Start by tracing the existing use of window.location.hash and the client-side navigation flow. Evaluate the HTML5 History API demo linked in the issue, then verify that navigation updates the URL, state, and title without reloading and that refreshing a generated-page URL does not land on an invalid page.

Written by the indexing model from the issue text.