Metadata objects seem redundant #54

The metadata objects are in the specification presumably to allow third-parties to agree on additional metadata for any of the objects. I believe that this is redundant since the JSON schema doesn't have additionalProperties set to false anywhere, and the markdown doesn't seem to suggest otherwise. So, any third party tools are permitted to add optional properties to any object in their payloads and other third party tools can parse them out as optional without failing schema validation.

Removing metadata from being an explicit part of the OpenCLI specification will simplify parsers in typed languages where they will need reflective capabilities to convert arbitrary data types into JSON.