add AICc functionality back in

[juniperlsimonis]

AICc <- function(x, dat){
  ll <- logLik(x)
  np <- attr(ll, "df")
  nd <- dim(dat)[1] * dim(dat)[2]
  AIC <- AIC(x)
  pen <- (2*np^2 + 2*np)/(nd - np - 1)
  AIC + pen
}