onbeforenavigate redirect support

"redirect" is a common pattern. Ex: all external navigations go through "t.co"

How do you find the url user is navigating to inside onbeforenavigate handler?

Proposed API:
```
history.onbeforenavigate = (e) => {
  e.redirect(`newUrl?from={e.url}`)
}
```

POST requests cannot be redirected.
