Release notes

Changed type of Design.to_oxview_format from dict to str to keep convention with similar other methods such as Design.to_oxdna_format.

This is a breaking change, although the minor version number did not change. The method Design.to_oxview_json has the same functionality that Design.to_oxview_format, namely that it returns a JSON-serializable dict. Calling json.dumps on this dict produces the same output as Design.to_oxview_format.