Adjust header option handling to prohibit passing a value of 0 to align
with GNU numfmt. Also report header option parse errors as GNU does.
closes#1708
Align with GNU numfmt by trimming leading whitespace from supplied values.
If the user did not specify a padding, calculate an implied padding from
the leading whitespace and the value.
Also track closer to GNU numfmt’s error message format.
- refactor internal version specifications to be ">=M.m.p" (where M.m.p is *already published*)
## [why]
Loosening internal version dependencies decreases the coupling between packages such
that packages can be published in a looser order. It allows the packages to be version
updated and published in tandem (ie, by using `cargo workspace ...`). Once published,
the internal versions can then be updated (again, to an *already published* package
version), as needed.
