isForecast: isForecast
In nulloa/asgForecast: Importance Sampling with Assymetrical Gaussian Distribution

Preforms both types of importance sampling forecasting

1 2	isForecast(y, n.weeks, seas.fits, priors, prior.type = "Unif", n.iter, tau, sigma, samp_type = "Transformation")

`y`	data from forecast season
`n.weeks`	number of points from the forecast season to include
`seas.fits`	matrix season fits to be used in sampling (see `get_season_fit`)
`priors`	priors from `get_priors` or vector of means
`prior.type`	type of prior to use (default is "Unif)
`n.iter`	number of iterations to run
`tau`	scaling factor for est
`sigma`	sd used in generating weights
`samp_type`	Type of sampling procedure to be preformed