some better worked methods of conneg, although need to introduce the concept of strict/non-strict negotiation requirements to the machine graph now...
tidying some of the negotiation and machine logic (switching away from heavy operators) before evaluating extending the machine graph for better negotiation support
changing negotiation in machine to be more explicit about result, plus extending machine graph to allow strict regard to negotiation headers to be chosen (with hopefully suitable defaults)
Merge branch 'feature/conneg' into develop