Implement support for QFF_SPLIT_TIMESTAMP

I am very very unhappy with this patch. We have to do this, in order
to be compatible with the Python code and behaviour, but there's lots
of duplication; both the Python and the Haskell code will need to be
cleaned up and simplified (we don't need QFF_* at all).

For now though, this implements QffTimestamp and associated code.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>