Add Haddock /Since: 18.104.22.168/ comments to new symbols
These annotations were added in such a way, that the line
represents the last paragraph of the Haddock comment.
Maybe Haddock will have support for this meta-syntax at some point, and
be able to inherited the since-version property to the children of an
annotated symbol and display the since-version property in the rendered
documentation only in cases when it's not visually obvious (for
instance, when re-exporting documentation strings).
Signed-off-by: Herbert Valerio Riedel <email@example.com>