Changes in 0.3

  * New function: qml(), estimate single-class model with QML as an
    alternative to LMS
  * specify_sem(): model with num.classes = 1 will be of class
    'singleClass' now instead of 'lms'
  * Data set: jordan, PISA 2006 jordan sample
  * em(): Changed logger output for NSEMM models so readability is higher;
  added max.lms = 1 so EM for single groups will only iterate once

Changes in 0.2

  * specify_sem(): changed default for interaction to "none"; fixed bug so
  psi can be set to a fixed value now; changed default constraints
  * summary.emEst(): added weights to print method
  * em(): added error message when more than one eta is specified; put
  logger = TRUE as default

