Error overlay

[shuding]

It should support displaying error overlay (for both compilation and runtime errors) inside the iframe and send back the error with stack to the main window.

[huozhi]

Could also be a good chance to drop the returned error property. for sending back the error we might need to return a callback setter to receive it? Like

{ onError } = useLiveCode(files)

onError((e) => {
  ...
})

[shuding]

I think it should either take an onError callback as the argument or return an error value.