numfmt: a new command to format numbers

numfmt: a new command to format numbers

* AUTHORS: Add my name.
* NEWS: Mention the new program.
* README: Reference the new program.
* src/numfmt.c: New file.
* src/.gitignore: Ignore the new binary.
* build-aux/gen-lists-of-programs.sh: Update.
* scripts/git-hooks/commit-msg: Allow numfmt: commit prefix.
* po/POTFILES.in: Add new c file.
* tests/misc/numfmt.pl: A new test file giving >93% coverage.
* tests/local.mk: Reference the new test.
* man/.gitignore: Ignore the new man page.
* man/local.mk: Reference the new man page.
* man/numfmt.x: A new template.
* doc/coreutils.texi: Document the new command.