add support for event emit instead of flipKey

[scratchmex]

Maybe add support to force a refresh when emiting certain event instead of the component watching for the flipKey prop. I think this is more suitable for complex scenarios like large list or various components. At first I got trouble understanding the flipKey and I said, why we don't just give it a boolean and flip the value when we want it to refresh it!? but then I realized it will be more readable to support some emit('refresh'). I will be happy to start working on a PR draft but I want to start a discussion as well.

[mattrothenberg]

I don't think I understand the use case of this proposed imperative API.

Why can't you modify the value of flipKey to trigger an animation?