Returns 2-element list
* cbs: data.frame with 'cust', x, t.x, T.cal, 'T.star', 'x.star'
this is the summary statistics data.frame which contains all
needed information for parameter estimation
* elog: data.frame with 'cust', t
abe.GenerateData(n, T.cal, T.star, params, return.elog = FALSE)number of customers
length of calibration period
length of holdout period
list of parameters: beta, gamma
if TRUE then the event-log is returned as well; decreases performance
2-elemnt list