Pratical implementation of the validation of the parameters. The patch is quite long as it has a direct effect on the structure of the configuration dictionary. The validation has the advantage of automatically convert the parameters to the right type. Therefore rather than building a dictionary ourselves, we rather use the ready-made dictionary from ConfigObj. Because the names of the sections are not the same, quite a bit of code had to be adapted. Finally, note that the validation file containing the specification of each variable, pcigale.ini.spec, is created while building the pcigale.ini file. Also because it is needed to convert the data to the right type, one cannot run cigale without a correct validation file.