Add support for sending events/markers to a real SAS

Andy

As discussed can you review.  I've tested live and everything seems to get through okay and is searchable.  I need to do some more stress testing and testing of error cases (eg. when the SAS connection itself drops out and reconnects) but I want to get this level out asap.

I'll also be writing some UTs when I've worked out how best to scaffold it.

Mike