Get a string representation of all available datasets with descriptions.

def list_datasets():
    """Get a string representation of all available datasets with descriptions."""
    lines = []
    for name, resource in itertools.chain(LOCAL_DATASETS.items(), REMOTE_DATASETS.items()):

        if isinstance(resource, LocalFileMetadata):
            location = "local: {}".format(resource.filename)
        elif isinstance(resource, RemoteFileMetadata):
            location = "remote: {}".format(resource.url)
        else:
            location = "unknown"
        lines.append("{}\n{}\n{}\n{}".format(name, "=" * len(name), resource.description, location))

    return "\n\n{}\n\n".format(10 * "-").join(lines)