added file ppddl_effects to implement additional methods for the effect classes
added file ppddl_effects to implement additional methods for the effect classes

sandysa/mdp-lib,sandysa/mdp-lib,luisenp/mdp-lib,luisenp/mdp-lib,luisenp/mdp-lib,sandysa/mdp-lib,sandysa/mdp-lib,sandysa/mdp-lib,luisenp/mdp-lib,luisenp/mdp-lib