magit-create-branch-hook: new hook variable

In `magit-create-branch' explicitly run the new (but unadvertised) hook
`magit-create-branch-hook'.  This is a replacement for the automatically
run `magit-create-branch-command-hook'.  The latter will be removed soon.
magit-remote-update-hook: new hook variable

In `magit-remote-update' explicitly run the new (but unadvertised) hook
`magit-remote-update-hook'.  This is a replacement for the automatically
run `magit-remote-update-command-hook'.  The latter will be removed soon.
magit-pull-hook: new hook variable

In `magit-pull' explicitly run the new (but unadvertised) hook
`magit-pull-hook'.  This is a replacement for the automatically
run `magit-pull-command-hook'.  The latter will be removed soon.
magit-push-hook: new hook variable

In `magit-push' explicitly run the new (but unadvertised) hook
`magit-push-hook'.  This is a replacement for the automatically
run `magit-push-command-hook'.  The latter will be removed soon.
magit-define-command: remove macro
Merge branch 'pr/just-defun'