predict.bgnbd: Predict expected sales
In usobiaga/shopping: Probabilistic CLV models

Expected conditional sales in a t time period. E(Y(t)| X=x, t_x, T, r, α, a, b)

1 2	## S3 method for class 'bgnbd' predict(object, Tx, tx, n, t)

`object`	a object of class `bgnbd`.
`Tx`	lenght of time since the consumers first purchase.
`tx`	recency of the last purchase (time of the last purchase - time of the first).
`n`	count fo repeat purchases.
`t`	time period in which the expeted sales take place.