TODO
====

 * Written documentation in the form of a vignette. - DONE in 0.5-0
 * A formula method for 'mat' - DONE in 0.3-4
 * Thorough code review, testing and consistency checking - this will be the
   first widely advertised release.
 * Need to consistently have functions store DC Method as an attribute. Good to 
   write an extractor function and have all functions use that.
 * Speed-up distance() - move it to C - DONE in 0.12-0
 * plot.prcurve: needs to stop passing arguments on to other plotting functions.
 * Add a flexible GLM-based transfer function model which can do GLR plus
   other distributions for the response - particularly count models.
