seq- and jot-like enumerator

 enum enumerates values (numbers) between two values, possibly further adjusted
 by a step and/or a count, all given on the command line. Before printing,
 values are passed through a formatter. Very fine control over input
 interpretation and output is possible.
 .
 enum is designed to be a drop-in replacement for GNU seq while still providing
 (almost) the same feature set jot (on BSD) provides.