Merge docs/sphinx_autodocs into improve/V30RC01

The sphinx documentation should be up to date to v3.0 now.

• I suspect that the automatic part of the merge from improve/V30RC01 broke something that I am unable to find the exact problem, mypy complains about:

  aas\model\submodel.py:77: error: Incompatible types in assignment (expression has type "NamespaceSet[Constraint]", variable has type "Set[Constraint]")
  aas\model\submodel.py:139: error: Incompatible types in assignment (expression has type "NamespaceSet[Constraint]", variable has type "Set[Constraint]")
  

• There is a collection of docstrings that may need a rework in Issue #115 (closed).

For those who want to review the documentation, here is how you build it:

• Navigate to docs/
• Execute make html over the command line
• You can find the documentation in /docs/build/html/. The main page is called index.html.