libsmartcols: add ncols getter

Signed-off-by: Ondrej Oprala <ooprala@redhat.com>
libsmartcols: allow custom symbols

Signed-off-by: Ondrej Oprala <ooprala@redhat.com>
libsmartcols: supply missing getters/setters

Signed-off-by: Ondrej Oprala <ooprala@redhat.com>
libsmartcols: add scols_table_next_column

Signed-off-by: Ondrej Oprala <ooprala@redhat.com>