bgnbd.generalParams: Define general parameters
In BTYD: Implementing BTYD Models with the Log Sum Exp Patch

This is to ensure consistency across all functions that require common bits and bobs.

1	bgnbd.generalParams(params, func, x, t.x, T.cal, T.star = NULL, hardie = NULL)

`params`	BG/NBD parameters - a vector with r, alpha, a, and b, in that order. r and alpha are unobserved parameters for the NBD transaction process. a and b are unobserved parameters for the Beta geometric dropout process.
`func`	function calling dc.InputCheck
`x`	number of repeat transactions in the calibration period T.cal, or a vector of transaction frequencies.
`t.x`	time of most recent repeat transaction, or a vector of recencies.
`T.cal`	length of calibration period, or a vector of calibration period lengths.
`T.star`	length of time for which we are calculating the expected number of transactions.
`hardie`	if TRUE, use `h2f1` instead of `hypergeo` when you call this function from within `bgnbd.ConditionalExpectedTransactions`.