maint: autogenerate THANKS.

More automation == less time wasted on menial tasks.
* build-aux/thanks-gen: script inspired by coreutils.
* Makefile.am (THANKS): Based on rule from coreutils/Makefile.am.
* NO-THANKS: New file.  Configure thanks-gen output.
* THANKS: Remove.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: fix README-alpha version match.

With simplified release version numbering (thank you, git!), be
careful to recognize four part alpha versions, or short git
revision suffixed alpha versions correctly.
* Makefile.am (re_odd_version): Remove.
(re_alpha_version): Recognize alpha version numbers.
($(readme)): Adjust accordingly.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>