Support skinparams and class diagram syntactic sugar

[jjerphan]

Being able to specify skinparams as well as class diagram syntactic sugar for layout and arrow direction options for the output might be helpful.

Integrating it in the python API and reflecting it on the CLI needs first some design for usability.

I would be happy to work on this on my free time.

[lucsorel]

good idea, go ahead!

We can take time to discuss the current code design if it needs to be refactored.