Adds a new history entry and updates the browser's
address bar with the given URL.
When the user restores the new history entry later,
Unpoly will replace a selector from up.history.config.restoreTargets with the body from that URL.
Note that fragment navigation will automatically update the
browser's location bar for you.
Does not add a history entry if the the given URL is already the current browser location.
Emits event up:location:changed.
