Added ref-url, which may point to another json document containing the thing metadata.
Renamed uuid to id, to allow for localised id schemes which might not consist of uuids.
Merge branch 'master' of github.com:garyhodgson/thing-tracker-network
Merge branch 'master' of https://github.com/derrickoswald/thing-tracker-network into derrickoswald-master
Merge remote-tracking branch 'upstream/master'
Fix directory issue.