This PR does multiple things:
- the kinds are changed from custom objects to a proper enum.Enum class
(including according changes to the cython code and the kind generation scripts)
- all examples and tests are modified to account for the change how to use kinds
(Kind instead of kinds)
- add docstrings to the kind enum values
- add a custom documenter that properly renders enums via autodoc
- extend doxygen setup so that we can write comments as rst (allowing us to copy
the documentation for kinds from the cpp api to the other apis)
This PR includes documentation for the z3py compatibility API into our general API.
It does so by adding the z3py compatibility API as an external project to download it and then have sphinx document it via the autodoc extension that we already use for our regular python API.
Right now we simply show everything on one page, which should be refactored in the future.
