Metrics: MSE and Success Ratio of Forecasts
In ZehuaWu/gtm: Functions for Economic Nowcasting with Google Trends Data

This function calculates mean squared error (MSE) and the success ratio of a given set of forecasts.

1	Metrics(pred=NULL, true=NULL, h=0)

`pred`	vector of forecasts.
`true`	vector of true values.
`h`	forecasting horizon used in making the forecasts. Default is `0`.

This function returns the same outputs as does the maeforecast function. More specifically, it returns a list containing the following objects:

`Forecasts`	data matrix, containing the point forecasts, realized values, forecast errors, signs of the forecasts and realized values, and success in predicting the signs.
`MSE`	numeric, mean squred error of the point forecasts.
`SRatio`	numeric, success ratio of the point forecasts. Success is claimed when the point forecasts and realized values have the same sign.