Stretch flags over multiple lines

[yunruse]

It would be a useful addition to be able to control how a flag can be stretched. For example, --pan -n 1 would hit three lines and repeat, whereas --pan -n 3 would cover a 9-line file.

It might have problems with multiple flags, but I think that using both multiple flags and custom stretching might be beyond the scope of what would realistically be needed :p