fdformat: Add new switches -f/--from, -t/--to, -r/--repair

This commit introduces a support for user configurable
from/to track and a basic repair mode for broken floppies.
It also fixes a recently introduced bug that causes
a line breakage when printing the track number.

Signed-off-by: Karel Zak <kzak@redhat.com>
fdformat: clean up usage()

Signed-off-by: Karel Zak <kzak@redhat.com>