Downloads pre-compiled models from the circus-repository.
The circus-repository contains a variety of fitted models to help
the systematic testing of other packages
A model from the circus-repository, or NULL if model could
not be downloaded (e.g., due to server problems).
Arguments
name
Model name.
url
String with the URL from where to download the model data.
Optional, and should only be used in case the repository-URL is
changing. By default, models are downloaded from
https://raw.github.com/easystats/circus/master/data/.