Support multiple annotations on the same triple.

[pchampin]

Now that annotations introduce an intermediate reifier node,
it would make sense to allow multiple annotation "blocks" on a given asserted triple. E.g.

:liz :spouse :richard {| :w1 | :in 1964 |}
                      {| :w2 | :in 1975 |}.

[afs]

There has been a discussion to encourage blank nodes - this syntax addition doesn't have use explicitly named intermediate nodes:

:liz :spouse :richard {| :in 1964 |}
                      {| :in 1975 |}.