Exponential smoothing

Other than to improve the code here is what needs to be done
TODO
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[]Add Holt double Exponential smoothing
[]Add time series decomposition
[]Fix Holt Winters Additive model (just an if statement and change
                                    seasonal calculation from division to
                                    addition)
[]Add/improve Forcasting for Holt Winters to take multiple variables
  []Add confidence intervals to forcast
[]Add solver to fit Holt Winters parameters
[]Improve data summary RMS error, Sum of Square Residual,
[]Add pandas wrapper