added __str__ function for Graphs - which returns provenance metadata in n3 - as well as an ontology for the provenance terms used by __str__
added __str__ function for Graphs - which returns provenance metadata in n3 - as well as an ontology for the provenance terms used by __str__

yingerj/rdflib,RDFLib/rdflib,dbs/rdflib,avorio/rdflib,dbs/rdflib,ssssam/rdflib,avorio/rdflib,armandobs14/rdflib,RDFLib/rdflib,marma/rdflib,ssssam/rdflib,armandobs14/rdflib,yingerj/rdflib,dbs/rdflib,RDFLib/rdflib,yingerj/rdflib,ssssam/rdflib,armandobs14/rdflib,marma/rdflib,avorio/rdflib,yingerj/rdflib,armandobs14/rdflib,marma/rdflib,RDFLib/rdflib,ssssam/rdflib,dbs/rdflib,avorio/rdflib,marma/rdflib