bug#19113: Generate a ChangeLog file from commit logs

[Glenn Morris]

I think this change will lower the quality of Emacs ChangeLogs, which
are important forms of documentation; and frankly I don't even see that
it will save much work. But I'm obviously in a minority, so don't let me
stop you. I do have a list though; do whatever you like in response to it.

1) There are still things to deal with from the last big change, so I'd
appreciate it if you not do this before January at the earliest.

2) Announce the change well in advance, and make it very clear what
people need to do (ie, take much more care with their logs than before).
Put a clear set of instructions in admin/notes. Eg how will I replace `C-x
4 a', `C-c C-a' now? (Frankly I expect to keep doing that, just not
commit the ChangeLog, so as I said, I can't see that this will save any
effort). I hope the answer isn't "install vc-dwim", since Emacs is
supposed to contain all the necessary VC tools itself.

3) How will I mark a change so that it does not generate a ChangeLog?
(Examples include: NEWS edits, comment fixes, fixing a paren typo in
something I committed one second earlier.) Perhaps a "#" or somesuch in
the first char of the log? How will I do this after committing if I
forgot to so mark it at the time?

4) What if I commit something, realize it was wrong, and remove it right
away? Normally I'd delete the ChangeLog entry too.

5) Will I be able to mark a portion of a log to be excluded from the
generated ChangeLog?

6) How does the correction method work (I'm being lazy and not reading
the patch). (Since notes are editable comments associated with commits,
I like the idea of using notes to correct faulty logs.) Frankly, I
expect there to be lots of mistakes, but whatever; I'm not going to
bother to correct them anymore.

7) What dates will entries get? The commit date? This may not match the
push date. What will happen with the dates of entries merged from other
branches.