Merge branch 'tg/deprecate-stash-save'

"git stash save" has been deprecated in favour of "git stash push".

* tg/deprecate-stash-save:
  stash: remove now superfluos help for "stash push"
  stash: mark "git stash save" deprecated in the man page
  stash: replace "git stash save" with "git stash push" in the documentation