Create Logger backend

We had a request for logging errors during test runs. Per this conversation (via @ioquatix):

https://twitter.com/ioquatix/status/1318312887547408384

One way we could solve this is to add another backend option, perhaps a `Logger` backend. Instead of reporting on the `notify` method, we can log the error to stderr. We should also log the `check_in` id as well.