added deep iteration functionality to the _.add method
added deep iteration functionality to the _.set method
added deep iteration functionality to the _.sample method
added deep iteratoin functionality to the _.setUndef method
added deep iteration functionality to the _.keys method
added deep iteration functionality to the _.find method
added deep iteration functionality to the _.findKey method
removed collection type checking from _.empty
added deep iteration functionality to the _.contains method
added deep iteration functionality to the _.clone method
added deep iteration functionality to the _.has method