* Add explanation to help text and flag usage text
* KV get with new mount flag
* Clearer naming
* KV Put, Patch, Metadata Get + corresponding tests
* KV Delete, Destroy, Rollback, Undelete, MetadataDelete, MetadataPatch, MetadataPut
* Update KV-v2 docs to use mount flag syntax
* Add changelog
* Run make fmt
* Clarify deprecation message in help string
* Address style comments
* Add `kv rollback`
Like `kv patch` this is more of a helper than anything else; it provides
a single command to fetch the current version (for CAS), read the
version you want to roll back to, and set it as the new version (using
CAS for safety).
