* 2010-03-02: create a ConTeXt environment for holding all chapters
              of the accompanying textbook
* 2010-03-01: convert all chapters from LaTeX to ConTeXt
* 2010-02-25: add discussion around tetrachoric correlation in chapter
              3; correct typo. All file are now licensed under CCnSA
              (http://creativecommons.org/licenses/by-sa/2.0/)
* 2010-02-21: work on chapter 1, mainly on psychophysics; still a lot of
              work to do...
* 2010-02-16: begin chapter 5 with the application ('bfi' data from   
              psych); complete somehow chapter 2
* 2010-02-14: begin chapter 7 on IRT and select relevant articles/book
              chapters
* 2010-02-11: Rework chapter 3 on reliability. Put examples and theory
              on reliability and LM that should move in a separate
              chapter in the near future (probably that devoted to
              correlation analysis).
* 2010-02-06: added slides for content validity (chapter 4).
* 2010-01-31: added slides for content validity (chapter 4).
* 2009-11-04: almost finish chapter 3 (in its short version); work on
              the R package.
* 2009-11-03: work on chapter 3; design a set of handful Latex macros.
* 2009-11-02: first draft of chapter 3.