We decided we want to ship the pythonic API together with our base python API.
This PR adds a new target cvc5_python_api that first builds the base python API and then copies the pythonic API over. Furthermore we now use the cvc5.pythonic module to generate the corresponding documentation.
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.
