checkCVArguments: Validate that CV window parameters are valid
In forecastHybrid: Convenient Functions for Ensemble Time Series Forecasts

Validate that CV window parameters are valid

1	checkCVArguments(x, windowSize, maxHorizon)

`x`	the input time series.
`windowSize`	length of the window to build each model. When `rolling == FALSE`, the each model will be fit to a time series of this length, and when `rolling == TRUE` the first model will be fit to a series of this length and grow by one each iteration.
`maxHorizon`	maximum length of the forecast horizon to use for computing errors.