Add Importance Ratio as diagnostic for checking accuracy of normal approximation to posterior
See e.g. Slide 32 of http://apps.eui.eu/Personal/Canova/Teachingmaterial/bayes_dsge_eui2012.pdf
See e.g. Slide 32 of http://apps.eui.eu/Personal/Canova/Teachingmaterial/bayes_dsge_eui2012.pdf