Add Citation to Journal of Statistical Software paper

• Add Citation file for new JSS publication
• Correct minor bugs

Change interface of fitting function and add arima forecasting

StMoMo v0.4.0

• Upgrade plotting function of forecast models (plot.forStMoMo)
  to include nice fan charts similar to those in the forecast
  package
• Change inteface of fit function (fit.StMoMo) to allow
  simiplified calling using newly defined StMoMoData class
• Add the possibility of using general arima models (beyond the
  random walk with drift) for the forecasting and simulation of
  the period indexes
• Add new estimation function for the Renshaw and Haberman model
  implementing the approximate constraint Hunt and Villegas (2015)

Minor update to StMoMo

StMoMo v0.3.1

• Change residual plotting function (plot.resStMoMo) to use a
  more effective divergent colour palette for colourmaps.
• Change the default plotting limits in residual plotting
  function to have a symmetric scale
• Fix formatting issues in logLik, AIC and BIC functions for
  models fitted with gnm

Minor update to StMoMo

StMoMo v0.3.0

• Add optional parameters kt.lookbacak and gc.lookback to
  functions forecast.fitStMoMo, simulate.fitStMoMo and
  simulate.bootStMoMo. These new parameters allow the forecast
  and simulation of mortality models using only a limited history
  of the period and cohort indexes
• Improve documentation of some functions
• Update package vignette
• Add citation file

First stable version of StMoMo

First accepted submission to CRAN