Define version compatibility behavior

[Carolyn Van Slyck]

Now that we have a new version of the core spec, 1.0.1, what behavior can people rely upon when the version that the bundle was built against doesn't match what the tool they are using to run it supports?

Examples:

• Forwards Compatibility They are still using an old duffle binary that was built for 1.0.0 and are running a bundle built for 1.0.1
• Backwards Compatibility They are using a bundle built for 1.0.0 and the latest duffle which supports 1.0.1

The behavior should be defined in https://github.com/cnabio/cnab-spec/blob/master/901-process.md#versioning