The function (ReadSortFile()) reads a csv file of free sorting data.
The file contains stimuli as rows and subjects as columns. For a subject, two stimuli in the same group are coded by the same symbol. First row contains the labels of subjects and first column contains the labels of stimuli.
For each subject, the coding of a group may be a number or a list of terms describing the group (terms have to be separated by a symbol, as a comma).
Returns a matrix of sorting and, if this is adequate, matrices describing the use of terms by subjects.