brms 1.3.1

new features

• Introduce the auxiliary parameter disc
  ('discrimination') to be used in ordinal models.
  By default it is not estimated but fixed to one.
• Create marginal_effects plots of
  two-way interactions of variables that were
  not explicitely modeled as interacting.

other changes

• Move rstan to 'Imports' and Rcpp
  to 'Depends' in order to avoid loading rstan
  into the global environment automatically.

bug fixes

• Fix a bug leading to unexpected errors
  in some S3 methods when applied to ordinal models.