This feature is experimental and not part of Unpoly's stable API.
It may be removed or changed without prior notice or deprecation.
Adds a new history entry and updates the browser's
address bar with the given URL.
When the user navigates to the added history entry at a later time,
replace the document body with
the body from that URL.
Note that functions like
up.submit() will automatically update the
browser's location bar for you.
The URL for the history entry to be added.