hubData 2.2.0

• Fixed bug in load_model_metadata() that caused array-valued top-level fields in model metadata YAML files to parse incorrectly or fail to parse at all (#137). Array-valued top-level fields are now translated into list columns, per the function specification. Note: The bug also meant that length-1 top-level arrays parsed equivalently to top-level scalars, e.g. both y: "x" and y: ["x"] parsed as a character column y with value x. With the fix, those entries parse differently: y: "x" parses as a character column; y: ["x"] parses as a list column. Thanks @dylanhmorris.