Allow error to propagate from preview

[elevatebart]

Following #33, it could be useful to naturally throw exceptions out of the vue-live component.
This would allow people to use error boundaries.

CC @codebender828

[codebender828]

Thank you so much @elevatebart . Can I find the updated API in docs?

[elevatebart]

I have not updated the readme yet. But there in an example if you look at app.vue