v0.2.9

• Switch from compiling Stan models at install time to compiling them at
  runtime, avoiding an Rcpp module issue.
• Add model argument to dgirt() and dgmrp() taking for reuse a previously
  compiled Stan model, as found in the @stanmodel slot of a dgirt_fit- or
  dgmrp_fit-class object.
• The version argument to dgirt() and dgmrp() can be used to specify
  arbitrary .stan files on the disk in addition to those included with the
  package.
• Argument by to get_n() and get_item_n() methods properly accepts a
  vector of variable names when combined with aggregate arguments.