Invoke operation with RdfResource or Dataset

[tpluscode]

The invoke methods should allow calling with an RdfResource or DatasetCore object and the underlying dataset would be serialised with formats-common

The question is how the forma would be selected. Maybe an OPTION would be required to look for accept header?

Alternatively, if a headers object is provided (directly of through defaultHeaders, then content-type should be the explicit selection of the serialiser to use