Added documentation

configure.ac

src/descriptor_identifier/Model/Model.hpp

src/descriptor_identifier/SISSORegressor.hpp

src/feature_creation/node/FeatureNode.cpp

src/feature_creation/node/FeatureNode.hpp

src/feature_creation/node/Node.hpp

src/feature_creation/node/operator_nodes/OperatorNode.cpp

src/feature_creation/node/operator_nodes/OperatorNode.hpp

...re_creation/node/value_storage/nodes_value_containers.hpp

src/feature_creation/units/Unit.hpp