bug#20898: 25.0.50; Move landmark.el to elpa

[Nicolas Richard]

A bit of searching shows that landmark.el is not used much (if at all),
and in fact causes confusion :
https://lists.gnu.org/archive/html/emacs-devel/2006-04/msg00294.html
https://lists.gnu.org/archive/html/emacs-devel/2014-06/msg00592.html

In that thread, Stefan suggests to move landmark.el to GNU elpa. I want
to give this a try. What's the procedure ?

My current plan is :
- move the file to lisp/obsolete/,
- add a note to lisp/obsolete/landmark.el that it moved to GNU Elpa
  (like what was done for crisp.el)
- mention these changes in ChangeLog and NEWS
- copy the file to elpa.git, as packages/landmark/landmark.el
- add a Maintainer header (who should that be ? the original author ?)
and that's about it.

Opinions and advices very welcome.