Rename 'gencsv' to 'gendsv'

It can generate both CSV and TSV files.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Deduce format from filename in 'gendsv'

If the extension is '.tsv', use a tab character as the separator.
Otherwise use a comma as the separator.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>