* notifications.el (notifications-specification-version): Change to "1.2".

* notifications.el (notifications-specification-version): Change to "1.2".
(notifications-notify): Add :action-items, :resident and
:transient hints.  Change "image_data" to "image-data" and
"image_path" to "image-path".
(notifications-get-capabilities): Return a list of keywords.

* os.texi (Notifications): Extend possible notification hints.