doc: improve version-sort doc

doc: improve version-sort doc

* doc/coreutils.texi, doc/sort-version.texi:
Capitalize “Coreutils”.
* doc/sort-version.texi: Don’t emphasize natural sort so much,
since Coreutils has just version sort.
Use the term “lexicographic” instead of “alphabetic” or “standard”.
Suggest combining ‘V’ with ‘b’, and show why ‘b’ is needed.
Use shorter titles for sections, as GNU Emacs displays info poorly
when titles are too long to fit in a line.
Use @samp instead of @code for samples of data.
Do not use @samp{@code{...}}; @samp{...} should suffice and
double-nesting looks bad with Emacs.
Omit blank lines in examples that would not be present
in actual shell sessions.
Quote with `` and '', not with " or with '.
Mention dpkg --compare-versions more prominently.
Don’t rely on "\n" being equivalent to "\\n" in shell args.
Prefer Unicode name for hyphen-minus.