Add :name: option for referencing figure with :numref:

[pypamart]

Hello,

As a user, I want to use an reference option, In order to reference/cite my figure from the text or other document location.

Solution : add '"name": directives.unchanged' in the option_spec of Kroki class located at kroki.py file line 87.

Thank you.

[hason]

Fixed with #5