Update documentation for the C++ implimenation

src/descriptor_identifier/Model/Model.hpp

src/descriptor_identifier/SISSORegressor.hpp

src/feature_creation/feature_space/FeatureSpace.hpp

src/feature_creation/node/FeatureNode.hpp

src/feature_creation/node/ModelNode.hpp

src/feature_creation/node/Node.hpp

src/feature_creation/node/operator_nodes/OperatorNode.hpp

...ator_nodes/allowed_operator_nodes/absolute_difference.hpp

.../operator_nodes/allowed_operator_nodes/absolute_value.hpp

...eation/node/operator_nodes/allowed_operator_nodes/add.hpp

...eation/node/operator_nodes/allowed_operator_nodes/cos.hpp

...ation/node/operator_nodes/allowed_operator_nodes/cube.hpp

.../node/operator_nodes/allowed_operator_nodes/cube_root.hpp

...ion/node/operator_nodes/allowed_operator_nodes/divide.hpp

...ode/operator_nodes/allowed_operator_nodes/exponential.hpp

...eation/node/operator_nodes/allowed_operator_nodes/log.hpp

...n/node/operator_nodes/allowed_operator_nodes/multiply.hpp

...tor_nodes/allowed_operator_nodes/negative_exponential.hpp

...eation/node/operator_nodes/allowed_operator_nodes/sin.hpp

...ode/operator_nodes/allowed_operator_nodes/sixth_power.hpp