dataset v2.1 compatibility release

This release updates py_dataset to version v2.1.1 of libdatast from the dataset project. See release-notes-v2.1.1.md for changes. The are a number of function signatures that have update, some behavioral change in methods, depreciated functions and a few new ones. The versioning model changed in dataset between v1 and v2, this release reflects the new model. With it comes support for using SQL stores for the JSON objects as well as experimental versioning of objects and attachments based on a common increment setting for the semver.