AST-933 Add sphinx documentation

This builds sphinx documentation for a subset of C++ classes and python classes. The python documentation is not as complete as the C++ documentation, there will be a follow-up MR to fix that.

doc/tree/interfaces-overview.rst

 Interface overview
 ======================
 
-Radler is primarily written in :code:`C++`. In case Radler was compiled with :code:`BUILD_WITH_PYTHON=ON`
+Radler is primarily written in :code:`C++`. If Radler was compiled with :code:`BUILD_PYTHON_BINDINGS=ON`
 Python bindings are generated to interface the Radler API from within Python. See below for the documentation of the
 :code:`C++` and the :code:`Python` interface.