`navigate()` falls through to window.location on no matching route.

Per previous conversations with @ericf.
If this looks like an acceptable solution, I can add tests.

/cc @pdokas @jeremyruppel
Is there a reason for the option to be named `handleFallThrough` while the attribute is `handleFallThroughNavigation`? Is that a convention? Might be nice to have congruency here if it's not.