* Added -p <dir> command-line option to all programs: backend, cli, netconf, restconf.
* Moved and updated all standard ietf and iana yang files from example and yang/ to `yang/standard`.
* Renamed example yang from example.yang -> clixon-example.yang
* That is, limited support of: ietf-yang-library.yang
* For example: `<module><name>example</name><revision/></module><module><name>ietf-restconf-monitoring</name><revision>2017-01-26</revision></module>...`
* Comply to RFC 8040 3.5.3.1 rule: api-identifier = [module-name ":"] identifier
* The "module-name" was a no-op before.
* This means that there was no difference between eg: GET /restconf/data/ietf-yang-library:modules-state and GET /restconf/data/XXXX:modules-state