Add python documentation

cmake/TransferDocStrings.cmake

docs/Doxyfile.in

docs/conf.py

docs/index.rst

docs/make.log

docs/python_api/py_DescriptorIdentification.rst

docs/python_api/py_FeatureCreation.rst

docs/python_api/py_FeatureSpace.rst

docs/python_api/py_model.rst

docs/python_api/py_node.rst

docs/python_api/py_node_utils.rst

docs/python_api/py_solvers.rst

docs/python_api/python_api.rst

src/feature_creation/feature_space/FeatureSpace.hpp

src/python/bindings_docstring_keyed.cpp