do_get_tdisagg_matrix(): some improvements
GretlDataset::tdisagg() works for series; now we need some check for matricses
GretlDataset::tdisagg() works, but 's' param must be marked mandatory
do_get_tdisagg_matrix() implemented, let's try it out with GretlDataset
unused code deleted
GretlDataset: ::pad-daily() and ::unpad-daily() implemented
GretlDataset::resample() implemented, thought some issues related with subsample flag inside libgretl's modify_dataset()
GretlDataset: fix for dsortby()