[TASK] Documentation of hooks and jumpurl feature

Added documentation about available hooks in direct_mail
and hte privacy feature in jumpurl.

Resolves: #53171
Releases: 4.0
Change-Id: If5293a5a3540e8cb6d8043d4a2bba37ed300a961
Reviewed-on: http://review.typo3.org/33301
Reviewed-by: Ivan Dharma Kartolo <ivan.kartolo@gmail.com>
Tested-by: Ivan Dharma Kartolo <ivan.kartolo@gmail.com>