Changes in Version 0.2-0

  o Major update with new model fitting functions (partial credit and
    rating scale model) and improved infrastructure for conditional
    maximum likelihood estimation (C implementation of elementary
    symmetric functions).
    
  o Partial credit models (PCMs) can be fitted with the function
    PCModel.fit(). The interface and return value is similar to that
    of RaschModel.fit().

  o Rating scale models (RSMs) can be fitted with the function
    RSModel.fit(). The interface and return value is similar to that
    of RaschModel.fit() and PCModel.fit().

  o The function elementary_symmetric_functions() for computing ESFs
    is extended and now part of the exported user interface. The
    R implementation for binary items up to order 2 is complemented
    by a C implementation for both binary and polytomous items
    up to order 1.

  o Due to numerical instabilities in the coefficients and standard 
    errors between different architectures, the optimization method
    for Rasch/RSModel/PCModel.fit() was changed from nlm(...) to 
    optim(..., method = "BFGS"). Consequently, the arguments "reltol"
    and "maxit" are used now instead of "gradtol" and "iterlim". For
    backward compatibility RaschModel.fit() still supports the old
    arguments but might cease to do so in future releases.


Changes in Version 0.1-4

  o Added YouthGratitude data from Froh, Fan, Emmons, Bono, Huebner, Watkins
    (2011, PA), provided by Jeff Froh and Jinyan Fan. Some approximate
    replication code is provided in the examples (the parts depending on
    lavaan are in \dontrun).


Changes in Version 0.1-3

  o Fully exported elementary_symmetric_functions(). (An extended C
    implementation is under development and will be included in
    future releases.)


Changes in Version 0.1-2

  o Support of non-integer weights in btReg.fit(). To facilitate this,
    summary.paircomp() gained a weights argument so that optionally
    the weights are aggregated instead of observations counted.  
  
  o Actually pass on nlm() arguments from RaschModel.fit(). Also
    support iterlim = 0, i.e., set up model at pre-specified parameters.
  
  o Added StereotypeThreat data from Wicherts, Conor, Hessen (2005, JPSP),
    provided by Jelte M. Wicherts. Replication code is provided in the
    examples (the parts depending on lavaan are in \dontrun).


Changes in Version 0.1-1

  o New "psychotools" package containing all 'base' infrastructure
    previously contained in "psychotree". This is in order to provide
    both methods and data that can be reused by "psychotree" and
    the new package "psychomix" (as well as potentially further packages).
    
  o Classes: "paircomp" and associated methods.
  
  o Models: btReg.fit() and RaschModel.fit() and associated methods.
  
  o Data: Firstnames, GermanParties2009, Soundquality (previoulsy in
    psychotree) and VerbalAggression (new data, contained in other
    formatting in difR/verbal and lme4/VerbAgg).
