High Priority:
  default fixed effect prior on

Medium Priority:
  Fixef with non-zero mean
  Permit the permutation of scale matrices with named rows/columns to match that of the factor
  Unit test with priors on both covariance and fixef?
  Doxygen headers for functions
  sim
  Shift mean of intercept for priors unmodeled coefs so that it is effectively centered
  Vignette

Low Priority:
  Full unit tests for various priors, glm case
  Approximate optimization for common scale when there's a prior on the fixef
  t-priors on unmodeled coefficients
  Priors on the common scale
  Prove that way of handling Newton's method is correct
  Unify how positive definite matrices are handled from covariance and unmodeled coef parsers