caltechlibrary/dataset: Collection Metadata release

Added support for Namaste style metadata about collection (type, who, what, when, where, version and contact). The metadata is stored in the `collection.json` and Namaste are rended on `SaveMetadata()` calls. `SaveMetadata()` is now an exported function. There is now a concept of "dataset_version" versus "version". "version" is the semvar associated with the collection, "dataset_version" is the version associated with the "type" in Namaste as well as the version of the dataset command/library that wrote the collection. This is a breaking change with pre-v0.0.48 release. I have changed the Python module's `version()` function to reflect this. It is now called `dataset_version()`. The Namaste features are not implemented in the Python package but maybe in the future.