Add CGMES v3 support

[m-mirz]

The CGMES v3 seems to be available here but the schema files are still missing.

[chicco785]

@m-mirz is there any reason why v3 version is not yet supported? I think rdf profiles can now be found around :)

[dinkelbachjan]

We have the CGMES v3 RDFS documents now available here and intend to incorporate the corresponding Python classes generated by CIMgen into CIMpy

[iripiri]

The Python files for CGMES v3 are uploaded in a separate branch, open TODOs:

• adapt documentation
• add/adapt examples
• adapt cimexport.py
• add/adapts tests

[stv0g]

I am just curious about the existing PR #22.

Are you still planning to finish/merge it?

[m-mirz]

Yes, we should merge it. It looks like it is ready. I won't be able to check it before the weekend. So feel free to add your review :-)