Seq: Implement -f option

[marcospb19]

Is your feature request related to a problem? Please describe.
Our seq doesn't implement -f option, but it is necessary to be considered completed.

Describe the solution you'd like
Add a flag -f based on this:

seq [OPTION]... FIRST INCREMENT LAST

-f, --format=FORMAT
use printf style floating-point FORMAT.

FORMAT must be suitable for printing one argument of type 'double'; it defaults to %.PRECf if FIRST, INCREMENT, and LAST are all fixed point decimal numbers with maximum precision PREC, and to %g otherwise.