Add version field to data saver/ loader metadata

**Is your feature request related to a problem? Please describe.**
The data save and loaders return metadata. We should version this schema so that we can iterate and make changes-- people can then know how to version/write code against it.

**Describe the solution you'd like**
Add a `__version__` field or something. It should follow semantic versioning. Major = breaking. Minor = new addition. Patch = bug fix.

**Describe alternatives you've considered**
N/A

**Additional context**
N/A