brms 1.5.0

new features

• Implement the generalized extreme value
  distribution via family gen_extreme_value.
• Improve flexibility of the horseshoe
  prior thanks to Juho Piironen.
• Introduce auxiliary parameter mu
  as an alternative to specifying effects within
  the formula argument in function
  brmsformula.
• Return fitted values of auxiliary parameters
  via argument auxpar of method fitted.
• Add vignette "brms_multilevel", in which
  the advanced formula syntax of brms is explained
  in detail using several examples.

other changes

• Refactor various parts of the package
  to ease implementation of mixture and multivariate
  models in future updates. This should not have
  any user visible effects.
• Save the version number of rstan in
  element version of brmsfit objects.

bug fixes

• Fix a rare error when predicting von_mises
  models thanks to John Kirwan.