Stationary chisquare based on loglikelihood

[gotten]

Reported by Richelle van Capelleveen

The stationary chisquare is converted from the loglikelihood which has the additive normalisation term. This was fixed for the fitted chisquare in PR #63.

backtracks/backtracks/backtracks.py

Line 243 in e4e481a

self.stationary_loglike = self.loglike(self.stationary_params)