Add support for non-range emits

It's now possible to emit a point rather than a range per dimesnion.
So if you emit a 2-dimensional point, you no longer need to emit:

    emit([[doc.lon, doc.lon], [doc.lat, doc.lat]], null);

But you can simply do a:

    emit([doc.lon, doc.lat], null);

Change-Id: Ica542533e378222e76503edabf72fe57e589942c
Reviewed-on: http://review.couchbase.org/40371
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Volker Mische <volker.mische@gmail.com>