Add <Redirect/> component

[ryanflorence]

I've been thinking about this for a while, and I like it.

• URLs in an app change
• sometimes you want to defend against users deleting segments of a URL

<Routes>
  <Route name="dashboard" handler={Dashboard}/>
  <!-- we used to have `/home` but now we want `dashboard` -->
  <Redirect path="home" to="dashboard"/>

  <Route handler={User}>
    <Route name="user-details" path="user/:userId/details" handler={Details}/>
    <Route name="user-activity" path="user/:userId/activity" handler={Activity}/>
    <!-- guard against users deleting the `details` or `activity` segments of the url -->
    <Redirect path="user/:userId" to="user-activity"/>
  </Route>
</Routes>

This prevents devs from having to write a bunch of redirect code in handlers that don't need to exist. Maybe opens up some convention for us in server rendering to tell the dev to send the proper status code.
#149 is kindof related

[mjackson]

I'm 👍 on this. Should be fairly easy to implement given the current API as well. We already have transition.redirect().

[ryanflorence]

great opportunity to make RouteMixin too I think

[mjackson]

Yeah, but I'd prefer to stay away from naming stuff *Mixin. The mixin name should describe what it does, not what it is.

[ryanflorence]

yessir, I prefer the -able variants. Routable

[ryanflorence]

closed, follow #172 for updates