Allow optional host for matching

[Meisolsson]

Hi,

We ran into case where we would like preact-router to handle complete URL:s. For example we get a link like https://example.com/test from our CMS and when the user clicks it we would prefer if Preact handled that but it should not handle https://other-site.com/test. I propose a prop on the router which can be checked against like:

<Router host={'https://example.com'}>
   ...
</Router>