Represents ARFIMA models.
buildModel() passes on fitting and forecasting functions to FitModel's method setFittedFcasted
; applies Box-Cox transformation and bias-adjustment; ignores passing function which checks whether residuals are not independently distributed
useModel(fcast_period) calls FitModel's method executeUseModel
to fit model and forecast fcast_period
-step ahead future; passes on the same fitting and forecasting functions as buildmodel()