Lessen focus on ChangeLog files, as opposed to change log entries.

Lessen focus on ChangeLog files, as opposed to change log entries.

This is in preparation for generating the former automatically
from the latter.
* admin/notes/bugtracker, admin/notes/copyright, admin/notes/newfile:
ChangeLog -> change log
* admin/notes/changelogs: Remove, merging old contents to ...
* admin/notes/repo: ... here.
* doc/emacs/maintaining.texi (Change Log): Mention that ChangeLog files may
be copied to or from a version control system.
* doc/emacs/trouble.texi (Sending Patches): Point to the commit messages.
* doc/lispref/intro.texi (Acknowledgments): ChangeLog file -> change log entries.
* doc/lispref/tips.texi (Library Headers): Emacs uses a version control system.
* etc/CONTRIBUTE: Give advice about git commit messages and how
to generate proposed patches containing them.