change examples to meet CRAN tests - examples now
compute on mtcars instead of a data set that needs to be downloaded
adds gracefull error message in tests (all skipped on CRAN) when test data cannot be
loaded
summclust 0.7
fixes a bug that turned NA values in cluster variables not contained in the model call into a distinct cluster. Instead, summclust now throws an error.
summclust 0.6
support for regression weights / weighted least squares